Joe Biden tried to use arms sales to pressure Israel. It didn’t work.

U.S. arms sales to Israel are a potent symbol of Washington’s support for its closest Middle East ally, and potentially a powerful tool of influence over it.

With prospects for a cease-fire in Gaza hanging in the balance, the Biden administration is facing the political limits of that power.

The decision last week by the Biden administration to move forward with $20 billion in weapons deals for Israel after months of delays came just ahead of Secretary of State Antony Blinken’s trip to the Middle East in what many viewed as a last-ditch effort to get an agreement that will halt fighting in Gaza.

Blinken returned to Washington on Wednesday with no breakthrough, though talks are continuing.

State Department officials said last week’s announcement of weapons sales was decided independent of hopes for a cease-fire. But some inside the administration said they hoped the sales would signal that the U.S. is backing Israel amid concerns about a potential Iranian retaliatory attack in response to the recent killings of a senior Hamas leader in Tehran and a Hezbollah commander in Beirut.

The announcement also came while Congress is in recess, reducing the chances of public pushback by some Democratic critics.

The Biden administration may have intended to encourage Israeli Prime Minister Benjamin Netanyahu to embrace a cease-fire agreement, said Daniel Levy, a former Israeli government official. But that approach could ultimately backfire, he added, because when Washington provides weapons, Netanyahu feels that he has won, and “he can manage America as he always does.”

The sales announced by the administration last week include a fleet of F-15 warplanes, military vehicles, mortars, tank ammunition, and missiles. The State Department said delivery of most of the weapons wouldn’t begin until 2026, and not until 2029 in the case of the aircraft.

For decades, weapons have been a core component of the U.S.-Israel relationship. Israel is the recipient of more than $3 billion in annual military aid, and most of its weapons purchases are made with U.S. government funding.

In the more than 10 months since Hamas’s Oct. 7 assault on Israel, which according to Israeli authorities killed more than 1,200 people, the U.S. government has at times rushed arms to Israel, even using an emergency rule to send it artillery and tank shells. The U.S. has also delayed some sales without public explanation and paused one shipment of bombs hoping to encourage Israel to contain the conflict.

At the start of the current war in Gaza, the Biden administration organized an airlift of tens of thousands of bombs and other weapons to Israel. As civilian casualties in Gaza mounted, the Biden administration stopped accelerating those shipments, and then decided to withhold a single shipment of large bombs to pressure Netanyahu to scale back its plans for an attack on the city of Rafah in southern Gaza.

At least 40,000 people in Gaza have been killed since the start of the current conflict, according to Palestinian officials, whose numbers don’t say how many are combatants.

President Biden warned Israel in March that an attack on Rafah, where more than a million Palestinians were sheltering at the time, would cross a “red line.” Cutting off weapons wasn’t on the table, Biden said, but he left open the possibility that the U.S. might withhold some types of military assistance to Israel.

Israel overhauled its military plan for going into Rafah, which the Biden administration said was the result of the decision to withhold the heavy bombs. But most civilians still ended up fleeing the city, and deaths have continued.

The Biden administration lifted its hold on delivery of 500-pound bombs but continues to freeze shipment of 2,000-pound bombs. Some observers question whether holding the weapons really had a significant impact on Israel.

“Trying to have leverage at a time of war is the worst time because that is when a partner is the least likely to be directed by the administration,” a Republican congressional official familiar with the sale said. “Countries are not going to limit their war because the U.S. is trying to fight the war from Washington. That is the worst kind of micromanagement.”

The White House referred comment to the State Department, and the Israeli prime minister’s office didn’t respond to a request for comment.

“I know that our policy has not changed with respect to security cooperation with Israel. If anything, we recognize that the threats are more acute,” a State Department official said. “At the same time, at the highest levels, we are raising issues of civilian harm with Israel.”

Israel has continued bombing Gaza, resulting in a heavy toll on civilians. An Israeli airstrike on Aug. 10 on a school in Gaza City killed dozens of people. The Israeli military said the school was being used as a militant command post.

The civilian deaths have frustrated the Biden administration, but haven’t led to a fundamental change in policy in arms sales, U.S. officials say. State Department reports have found that Israel may have violated humanitarian law while using U.S. provided weapons, but stopped short of concluding that Israel violated international law, allowing sales to proceed.

Limiting arms sales to Israel is also politically difficult, because Netanyahu has proven adept at speaking directly to American lawmakers. “Fast tracking U.S. military aid can dramatically expedite an end to the war in Gaza and help prevent a broader war in the Middle East,” he said, speaking to Congress during a July visit.

The difficulties of using arms sales to influence policy goes beyond Israel, according to Rachel Stohl, a senior vice president of research programs at the Stimson Center, a Washington-based think tank.

“There is often no clear indication that weapon sales have changed the policies of the recipient country,” Stohl said. “What happens is we give implicit permission for countries to act in a certain way.”

Write to Nancy A. Youssef at nancy.youssef@wsj.com and Jared Malsin at jared.malsin@wsj.com