Three days after Hamas terrorists slaughtered more than 1,400 people, President Biden offered Prime Minister Benjamin Netanyahu support in the wake of the vow by Israel’s leader to “avenge this black day” and to turn Hamas hide-outs “into a ruin” from the air and on the ground.

“I told him if the United States experienced what Israel is experiencing, our response would be swift, decisive and overwhelming,” Mr. Biden recalled saying during a call between the two leaders on Oct. 10.

But the president’s message, in which he emphatically joined the mourning that was sweeping through Israel, has shifted dramatically over the past three weeks. While he continues to declare unambiguous support for Israel, Mr. Biden and his top military and diplomatic officials have become more critical of Israel’s response to the terrorist attacks and the unfolding humanitarian crisis.

The president and his senior aides still cling to the hope that the new war between Israel and Hamas might eventually give way to a resumption of talks about normalization of relations between Israel and Saudi Arabia, and could even offer some leverage for a return to negotiations over a two-state solution in which Israel and Palestine exist side by side. Mr. Netanyahu has long resisted such a move.

“Though it may seem a little bit more illusory now, we still believe it’s the right thing to do for the region, for the world, certainly for the Palestinian people,” John F. Kirby, a spokesman for the National Security Council, said on Monday.

But in the short run, American officials have grown more strident in reminding the Israelis that even if Hamas terrorists are deliberately intermingling with civilians, operations must be tailored to avoid nonmilitary casualties. Last week, Secretary of State Antony J. Blinken said at the United Nations that “humanitarian pauses must be considered,” a move that Israel has rejected.

“While Israel has the right — indeed, the obligation — to defend itself, the way it does so matters,” Mr. Blinken said, adding that “it means food, water, medicine and other essential humanitarian assistance must be able to flow into Gaza and to the people who need them.”

On Sunday, just a day after Israeli military leaders said Hamas terrorists were using a hospital in Gaza as a command center, Jake Sullivan, the president’s national security adviser, was more blunt. Mr. Sullivan said on CBS’s “Face the Nation” that Hamas’s use of civilians as human shields “creates an added burden for the Israeli Defense Forces.”

He added, “This is something that we talk about with the Israelis on a daily basis.” He then noted that hospitals were not legitimate military targets just as Israel was warning that another major hospital in Gaza had to be emptied out before the next round of bombing.

Administration officials said the shift in tone and substance was the result of the humanitarian crisis in Gaza, where the health ministry says more than 8,000 people have been killed, provoking outrage in the United States and around the world.