Mr. Gantz, a former chief of staff of the Israel Defense Forces who visited Washington last year, was scheduled to meet separately with Jake Sullivan, the national security adviser, his office said in a statement, as well as with members of Congress and pro-Israeli lobbyists.

U.S. officials told reporters over the weekend that negotiations were continuing and that Israel had “more or less accepted” a framework for the hostage deal, but also that Hamas had not yet accepted it. Hamas has rejected the proposal to release the more than 100 Israeli hostages because it does not include a permanent cease-fire and the withdrawal of Israeli troops from Gaza — concessions that Israel has said would prevent it from destroying Hamas.

In a statement, the office of Prime Minister Benjamin Netanyahu of Israel said it had not approved Mr. Gantz’s travel to Washington. An official in Mr. Netanyahu’s office, who spoke on the condition of anonymity, said Mr. Gantz did not represent the government on his trip to Washington and insisted that the prime minister continued to maintain open communication with Mr. Biden.

Mr. Gantz, however, told Mr. Netanyahu on Friday of his intention to fly to the United States to coordinate on messages he would convey in his meetings with American officials, Mr. Gantz’s office said in a statement on Saturday. Mr. Netanyahu’s displeasure was so firm that he told Mr. Gantz that he thought his plans were “counterproductive,” according to an Israeli official close to Mr. Gantz, who spoke on the condition of anonymity to discuss details of the call between the leaders.

Mr. Gantz’s trip is another representation of the divisions within Israel’s five-member war cabinet that burst into the open in January when Gadi Eisenkot, Mr. Gantz’s ally and fellow cabinet member, rebuked Mr. Netanyahu’s goal of achieving “total victory” in a television interview.

Key issues that Mr. Gantz and Mr. Netanyahu were wrangling over were how to address the future of Gaza and enlistment into the army, said Yohanan Plesner, the president of the Israel Democracy Institute, an independent research group. “As the war winds down, the differences over postwar priorities are being magnified,” he said.

Mr. Gantz is often floated as a possible future prime minister and is considered a top rival of Mr. Netanyahu, who has not visited Washington since the start of the war and whose relationship with Mr. Biden has encountered obstacles.

Ms. Harris’s aides have long felt that foreign policy is an opportunity for her to carve her own lane and shape a forceful role as vice president. The White House has also previously deployed Ms. Harris to speak about issues that galvanize young voters and voters of color. Ms. Harris is now trying to do both of those at the same time — using an urgent foreign policy issue to speak to a frustrated bloc of voters and carve out her own distinct political identity.

But some groups that have been calling for a permanent cease-fire said Ms. Harris did not go far enough. They said her remarks amounted to little more than invoking the rhetoric of those who have protested the war, without actually calling for a radical shift in policy that might change the situation.

Layla Elabed, the campaign manager of Listen to Michigan, the group that mobilized more than 100,000 voters to vote “uncommitted” against Mr. Biden in the Michigan primary, said in a statement that it was clear the administration was responding to pressure.

“But let’s be clear: This is a temporary cease-fire, or what they used to call a humanitarian pause,” Ms. Elabed said in a statement. “Our movement’s demands have been clear: a lasting cease-fire and an end to U.S. funding for Israel’s war and occupation against the Palestinian people.”

Adam Rasgon and Aaron Boxerman contributed reporting from Jerusalem.