Representative Joaquin Castro, Democrat of Texas, called it a “defining vote,” adding, “We’re either going to participate in the carnage, or we’re not.”

There is little doubt that the bill, which would send roughly $13 billion in military assistance to Israel as it continues its offensive in Gaza, will pass the House, along with money for Ukraine, Taiwan and other American allies.

But progressive Democrats estimated that 40 to 60 members of their party may oppose it on the House floor on Saturday. That would be a striking signal from Congress, where ironclad bipartisan backing for Israel has long been the norm. And it would highlight the fraught divisions the war in Gaza has sown within the Democratic Party, even as more Democrats including Mr. Biden have begun to criticize Prime Minister Benjamin Netanyahu’s approach to the conflict and urge him to better protect civilians.

The legislation would allocate $5 billion to Israel’s defense capabilities and $9 billion for “worldwide humanitarian aid,” including for civilians in Gaza. But it would not place further conditions on how Israel could use American military aid, nor block future arms transfers from the United States as an increasing number of Democrats have sought to do.

Democrats who are leading the push against the Israel aid bill said they strongly supported the Jewish state and its right to defend itself, and would vote in favor of sending military aid that supports Israel’s defense capabilities, such as by replenishing the Iron Dome, David’s Sling and Iron Beam defense systems. They also denounced the Oct. 7 terrorist attack by Hamas that prompted the war, and said the hostages taken by Hamas must be released.

But they argued that approving more offensive weaponry without conditions was an untenable moral and political position that would amount to an endorsement of Mr. Netanyahu’s prosecution of the war, including his intention to invade Rafah over the objections of the Biden administration. More than 33,000 people in Gaza have been killed since the start of the conflict, according to the health ministry there, and the population is facing a hunger crisis.

“I understand the need for defensive weapons for Israel, particularly in light of the attack by Iran,” said Representative Ro Khanna, Democrat of California, who ran his first campaign on an antiwar platform and helped lead efforts to end U.S. participation in the war in Yemen. “But there is no justification to provide bombs and weapons to Netanyahu to continue the war in Gaza that is killing thousands of innocent Palestinian women and children.”

Saturday’s vote will recall a similar situation from 2007, when the speaker at the time, Nancy Pelosi, Democrat of California, split a piece of spending legislation to allow Democrats to register their opposition to funding the Iraq war while backing a domestic funding bill. Speaker Mike Johnson, Republican of Louisiana, similarly divided the foreign aid package to be considered on Saturday in order to get each element across the finish line in the face of distinct coalitions of resistance to different pieces of the bill.

In a critical test vote on Friday, the House agreed, 316 to 94, to bring up the package, with 39 Democrats — mostly progressives — joining 55 Republicans in opposition.

“This is a moment for members of Congress who support a safe and secure Israel to send a message that giving Netanyahu more offensive weapons is not a path for peace and security for Israelis and Palestinians,” Representative Becca Balint, Democrat of Vermont and the first Jewish member of Congress to call for a cease-fire, said in an interview. “To give Netanyahu more offensive weapons at this stage, I believe, is to condone the destruction of Gaza that we’ve seen in the last six months. And it’s also a green light for an invasion of Rafah.”

Representative Lloyd Doggett, a Texas Democrat who led the opposition to funding for the Iraq war in 2007, said the conversations among Democrats in Congress opposing continued U.S. backing for the war in Gaza were “not unlike” those that took place 17 years ago.

“We may well be casting the vote on whether a much wider war takes place, and whether American weapons go that result in the death of thousands of innocent people,” Mr. Doggett said.

The Democrats who oppose the aid package for Israel represent a minority of their caucus. But they see a “no” vote as part of a strategy to pressure Mr. Biden to condition aid and halt future offensive weapons transfers. Through many meetings, text chains and conversations with the administration, they have worked to shift the president’s approach to Israel, while underscoring the electoral risks Mr. Biden faces among voters who helped power him to the White House in 2020 and are now furious over his handling of the war.

“The only way to get a course correction is for a sizable number within the Democratic caucus to say it must shift,” Ms. Balint said.

Representative Dan Kildee, a Michigan Democrat who has been pressing Mr. Biden to withhold offensive weapons from Israel, said a big “no” vote would strengthen the president’s hand to do so.

“It helps the administration to have some number of Democrats express ourselves in this way,” he said.

Representative Greg Casar, Democrat of Texas, said he hoped a substantial number of Democrats opposing the bill would give the Biden administration greater leverage to influence the Israeli government’s approach to the war.

“I hope this vote will show the world that there is a really significant segment of the United States that doesn’t want to see expanded and widening wars,” he said.

On Thursday, the military said it had also detained 600 people at the hospital. The Israeli accounts could not be independently verified.

The Al Jazeera news network and Wafa, the Palestinian Authority’s news agency, reported on Thursday that Israeli forces had blown up a building used for surgery that is one of the largest at the complex. The Israeli military said it had no comment on the reports.

Iyad Elejel, who lives about 500 yards from Al-Shifa, said the situation was “very terrifying,” adding in a phone call on Thursday: “We are hearing the constant sounds of clashes, gunshots, shelling, bombing, quadcopters and planes all day and all night.” Smoke had infiltrated the apartment where he is staying with 30 relatives, making it hard to breathe, he said.

Mr. Elejel said the children in the apartment were becoming used to the cacophony. “We try to convince them that the sounds they are hearing are from fireworks, but they don’t believe it,” he said.

Nobody has been able to leave the apartment since the raid began, Mr. Elejel said, and the family feared that they could run out of food soon. He said that when he looked out of his window Thursday morning, he saw “many dead bodies lying on the main street” out front. Israeli soldiers have been forcing people in the area to leave their apartments and head south, so the neighborhood was emptying out, Mr. Elejel said.

The military said in an earlier statement that it was continuing to “conduct precise operational activity in the Shifa hospital, eliminating dozens of terrorists over the past day during exchanges of fire.” It also said it was preventing harm to civilians and had located storage sites for weapons.

Mohammed Abu Kmail, a 35-year-old marketing consultant, said in an interview that he was with his wife and two daughters in their apartment, near the hospital, when they woke up before dawn Tuesday to the sound of gunfire close to their building.

He said that around 8 a.m., Israeli soldiers entered nearby buildings, and stripped and handcuffed about 25 men, including himself. He said that, after being scanned by a camera, he and some of the others were released. The account resembled those of other men detained in Gaza since the war began.

The Israeli military said in a statement that detained people “are treated in accordance with international law” and that “it is often necessary” to have detainees remove clothing so it “can be searched and to ensure that they are not concealing explosive vests or other weaponry.”

Israeli forces have carried out a series of raids on medical facilities in Gaza, arguing that Hamas has used them for military purposes. The armed group has denied doing so.

Israel made northern Gaza the initial target of its ground invasion of the enclave, which started on Oct. 27, and it first raided the hospital in November. It later provided evidence that Hamas had constructed a lengthy tunnel under the hospital. A later analysis by The New York Times found that Hamas had used the complex for military purposes. The Israeli military, however, has struggled to prove that Hamas maintained a command-and-control center under it.

Even before the current raid began, international aid workers said that the hospital barely functioned and was incapable of serving the acute health care needs of northern Gaza as it had before the conflict.

The World Health Organization had hoped to conduct a mission to the hospital on Thursday to provide fuel and food for staff and patients, as well as to assess the situation there, but permission had been denied because of security issues, according to Dr. Rik Peeperkorn, who represents the organization in Gaza and the West Bank.

The W.H.O. is “terribly worried” about the situation, he said, adding that it had not been possible to contact staff members there.

Israeli officials said earlier this week that Hamas personnel had returned to the hospital, prompting its operation. Military analysts said Israel’s decision to withdraw most of its forces from the north, in part to concentrate on defeating Hamas in other parts of Gaza, had in effect left a security vacuum.

The initial raid on Al-Shifa became a lightning rod for criticism of Israel over military action around hospitals and the danger it poses to patients and medical staff. The raid also became a symbol of a broader debate about the human cost of Israel’s military campaign to destroy Hamas in Gaza, in which tens of thousands of civilians have been killed or wounded.

Lauren Leatherby contributed reporting.

Although initial reports gave few details of the song, they sparked a furor on social media. Some Eurovision fans complained that the track was clearly referring to Oct. 7 and should not be allowed in the nonpolitical event in which pop stars, representing countries, compete against each other each May.

Since Eurovision began in 1956, the European Broadcasting Union, which organizes the contest, has forbidden songs that make political statements, insisting that the competition should unify, rather than divide. Every year, the union vets proposed lyrics to ensure they do not undermine that principle. Although Israel is not in Europe, its broadcaster is a member of the European Broadcasting Union, and therefore the country is eligible to compete in Eurovision.

On Wednesday, the news division of Kan, Israel’s public broadcaster, which oversees the country’s participation in Eurovision, reported that the broadcaster had begun discussions with the European Broadcasting Union over the suitability of “October Rain.” If the union refused to approve the track, the report speculated, Israel would not submit an alternative and would then be barred from the contest.

Miki Zohar, the country’s culture minister, said in a post on X on Wednesday that it would be “scandalous” if the song wasn’t allowed to compete.

In a letter sent to the European Broadcasting Union on Thursday, seen by The New York Times, Zohar put the case for “October Rain.” It was “an emotional song, discussing regeneration and rebirth,” he wrote. And while it reflected “the current public sentiment in Israel these days,” he said, that doesn’t make it “a political song.” (A spokesman for the minister said that Zohar hadn’t heard the “confidential” song, but had seen “a large part” of its lyrics.)

A European Broadcasting Union spokeswoman said in an email on Thursday that it was “currently in the process of scrutinizing the lyrics,” as it does for all proposed Eurovision tracks. “If a song is deemed unacceptable for any reason, broadcasters are then given the opportunity to submit a new song or new lyrics,” the spokeswoman added.

Even before this week’s uproar, Israel’s participation in this year’s Eurovision, which will be held in Malmo, Sweden, had cast a shadow over the event. As the death toll from Israel’s military offensive in Gaza has mounted, hundreds of musicians in countries including Sweden, Denmark and Iceland have signed petitions urging the European Broadcasting Union to ban Israel, following a similar decision in 2022 to ban Russia after it invaded Ukraine.

The European Broadcasting Union has repeatedly dismissed the comparison between Israel and Russia. “We understand the concerns and deeply held views around the current conflict in the Middle East,” the union said in a statement this month, but Eurovision was “not a contest between governments.”

At this year’s Eurovision, Israel will be represented by Eden Golan, a 20-year-old pop singer who was selected earlier this month when she won a TV talent show called “Rising Star,” singing an Aerosmith cover. During that show’s final, Golan referred to the roughly 130 hostages Israel believes Hamas is holding in Gaza. “We won’t truly be OK until everyone returns home,” she said.

Which song Golan will sing at Eurovision, however, is not only up to her. Kan has been evaluating potential tracks, and although it submitted “October Rain” for approval, the broadcaster is not scheduled to officially announce Israel’s song until March 10, allowing time for it to be changed, if necessary.

Throughout Eurovision’s history, the European Broadcasting Union has occasionally intervened when it detected political overtones in proposed entries, said Chris West, the author of a history of Eurovision. In 2009, he said, Georgia pulled out of the contest because the organizers objected to a song called “We Don’t Wanna Put In.” The song was seen as a statement against President Vladimir V. Putin of Russia, West said.

And in 2015, Armenia changed the title of its entry “Don’t Deny,” because it was widely interpreted as a reference to Turkey’s denial of the Ottoman Empire’s genocide of Armenians. The song was renamed “Face the Shadow,” West said.

“October Rain” seemed political from its title, West said, but Israel might claim it has nothing to do with last year’s attacks, or even that the country has a right to sing about the impact of Hamas’s atrocities.

“Eurovision’s organizers have a really difficult job of deciding where the line is,” West said.

Israel wants to demolish many of the Palestinian buildings close to the border in order to create what they describe as a “security zone,” according to the three officials, who spoke anonymously because they were not authorized to speak publicly about the issue.

Two of the officials said that Israel’s goal was to create a buffer of up to roughly six-tenths of a mile along the entire length of Israel’s roughly 36-mile border with Gaza. At its narrowest point, the territory is less than four miles wide.

Their intention is to make it harder for militants to repeat a raid like that of Oct. 7, in which roughly 1,400 people were killed and abducted, according to Israeli estimates, and which prompted the evacuation of tens of thousands of residents of southern Israel. One of Israel’s war goals is to create conditions that will persuade Israeli evacuees that it is safe to return home. Some of the demolished areas are a few hundred yards from Israeli neighborhoods that were attacked.

Asked about the creation of a buffer zone, the military said its forces were “locating and destroying terror infrastructures embedded, among other things, inside buildings,” which it said was necessary to implement a defense plan for southern Israel.

The military’s chief spokesman, Rear Adm. Daniel Hagari, said in a news briefing on Tuesday that the soldiers who were killed had been involved in an operation to “create the security conditions for the return of the residents of the south to their homes.’’

The idea of a buffer zone gained such momentum in Israeli discourse that the State Department spoke out against it in December, because it would effectively reduce the size of Gaza, a process opposed by the U.S. administration.

John Kirby, a spokesman for the National Security Council, repeated that objection on Tuesday, when asked at a White House news briefing about Israel’s moves to create a buffer zone. “We do not want to see the territory of Gaza reduced in any way,” Mr. Kirby said. “We won’t support that.”

However, Secretary of State Antony J. Blinken, speaking during a visit to Nigeria, said that the United States was open to a temporary buffer zone, though solely to enable Israelis who had fled homes along the Gaza border after Oct. 7 to return.

“If there need to be transitional arrangements to enable that to happen, that’s one thing to happen,” Mr. Blinken said. “But when it comes to the permanent status of Gaza going forward, we’ve been clear, we remain clear about not encroaching on its territory.”

To Palestinians, the practice is cruel and would keep Gazans in an already crowded enclave from being able to return to their homes. Critics of Israeli policy say the practice is part of a wider disregard for civilian housing and property. The majority of Gaza’s buildings have been damaged during the war, according to United Nations estimates, and more than 25,000 Gazans have been killed, according to Gazan officials.

Balakrishnan Rajagopal, the United Nations special rapporteur on the right to adequate housing, said a systematic demolition of Palestinian border homes could constitute a war crime because they pose no immediate threat to Israel.

“There is simply no provision in the Geneva Conventions for what Israel is doing along the border, which is kind of a pre-emptive clearing of property,” Mr. Rajagopal said in a phone interview.

“On a particular property by property basis, Israel can take action — but not on a widespread basis across the entire border,” Mr. Rajagopal said. “Israel, as the occupying power, has an obligation not to engage in what’s called wanton destruction of property.” The military did not respond to a request for comment on the claims.

While Israel has never formally announced the demolition of Palestinian border homes, the concept of a buffer zone lining the length of the Gazan border has been widely discussed by the Israeli news media since early December, when the idea was reported by Reuters.

Israeli ministers have also hinted of plans to create such a buffer zone since the first weeks of the war. Eli Cohen, the foreign minister at the time, said that after the war, “the territory of Gaza will also decrease.”

Days later, Avi Dichter, the agriculture minister, spoke of creating “a margin” along the Gaza border. “No matter who you are, you will never be able to come close to the Israeli border,” Mr. Dichter said.

Gabby Sobelman, Rawan Sheikh Ahmad, Erica L. Green and Michael Crowley contributed reporting.