When Prime Minister Benjamin Netanyahu of Israel came to the United States recently for another round of tense talks with the Obama administration, he got a decidedly warmer welcome from one of the rising Republican stars on Capitol Hill, Representative Eric Cantor, the incoming majority leader of the House.

But while Mr. Cantor and other newly empowered Republicans are eager to promote themselves as Israel’s staunchest defenders in Washington, the reconfigured American political landscape is a more complex and unpredictable backdrop for Middle East peacemaking.

Scores of Tea Party-backed candidates are entering Congress, many of whom favor isolationist policies and are determined to cut American foreign aid, regardless of its destination. Rand Paul, the newly elected Tea Party-backed senator from Kentucky, bluntly told the American Israeli Public Affairs Committee, an influential pro-Israel lobbying group, that they were going to disagree about the need for foreign aid and suggested that they move on to other topics, according to a person briefed on the meeting.

“One of the first things Congressman Cantor can do is to make sure that his colleagues vote for aid to Israel,” said Senator Charles E. Schumer, Democrat of New York, who also met with Mr. Netanyahu.

Mr. Schumer and others worry that support for Israel in Congress, long a bipartisan article of faith, could become politicized in a way that will end up harming Israel’s interests. In the recent election, the administration’s Middle East policy became a partisan issue, seized on by several Republicans who pointed out that President Obama had tended to take a tougher line against Israel.

Allen West, a black Republican, focused on it with great success in a heavily Jewish coastal district of Florida. Representative John A. Boehner, the Ohio Republican who is the House speaker-designate, sent out fund-raising literature aimed at Jewish voters, criticizing the administration for its pressuring of Israel on issues like settlements.

“That was the first time I had seen Israel used in a partisan political way,” said Representative Gary L. Ackerman, a New York Democrat and outgoing chairman of the House foreign affairs subcommittee on the Middle East and South Asia.

As a practical matter, lawmakers do not have the kind of leverage over Middle East policy that they have on matters that require Congressional approval, like the arms treaty with Russia currently being blocked by Senate Republicans, or big-ticket appropriations, like the health care law.

But Congress is far from powerless. Lawmakers can apply pressure on the margins, by attaching strings to financing for the Palestinian Authority; pushing for tougher sanctions against Israel’s hostile neighbor Iran; or by questioning weapons sales to Arab states.

And they can club the White House in the court of public opinion, as they did last April when nearly two-thirds of the members of Congress signed letters to Secretary of State Hillary Rodham Clinton urging the administration to defuse tensions with Israel over settlement construction.

While the White House did not back down from its demands, Mrs. Clinton subsequently gave two conciliatory speeches to Jewish groups, reaffirming the American commitment to Israel’s security.

With powerful friends like Mr. Cantor, a Virginia Republican and one of the highest-ranking members of Congress, the Israeli government was viewed by some as one of the big winners of the midterm elections.

The Republican-controlled House, analysts say, will be more inclined to defend Mr. Netanyahu, even against Mr. Obama, who has repeatedly clashed with the prime minister over the president’s demand that Israel freeze settlements to advance peace negotiations with the Palestinians.

“The administration has to take into account that Israel now has a friendlier forum,” said Abraham H. Foxman, national director of the Anti-Defamation League, a Jewish advocacy organization. “It will therefore think carefully about doing things.”

Mr. Netanyahu’s post-midterm election tour of the United States seemed to reflect his more powerful political backing. He delivered a speech calling on Mr. Obama to harden his policy toward Iran. And when the president voiced measured criticism of Jewish housing in contested East Jerusalem, Mr. Netanyahu’s office fired back a defiant response.

The night before Mr. Netanyahu met with Mrs. Clinton in New York to try to salvage Middle East peace talks, he sat down with Mr. Cantor in his hotel suite. The two men discussed the Republican triumph in the elections and the “existential threat” that Iran posed to Israel, Mr. Cantor said.

“It is my strong belief that U.S. security goes hand in hand with Israeli security,” Mr. Cantor said in an interview. “Whether this administration puts this into practice or not is another question, but that is the stated position of the administration.”

Yet the Tea Party-backed lawmakers remain something of a mystery. One of their brightest stars, Marco Rubio, went on a personal trip to Israel days after winning his Florida Senate race. But pro-Israel analysts point out that Mr. Paul once said he did not view an Iran with one nuclear bomb as a threat, though he has subsequently been more hawkish. Mr. Paul did not reply to a request for comment.

To be sure, there will be many other Republican voices staunchly in Israel’s corner. The incoming Republican chairwoman of the House Foreign Affairs Committee, Representative Ileana Ros-Lehtinen of Florida, is likely to push the administration even harder than her Democratic predecessor, Representative Howard L. Berman of California, to put sanctions into effect against Iran for its nuclear program.

Ms. Ros-Lehtinen and Mr. Berman recently sent a letter to Mrs. Clinton and Secretary of Defense Robert M. Gates challenging a $60 billion sale of advanced fighter jets and helicopters to Saudi Arabia. The deal has aroused concern in Israel, contributing to Mr. Netanyahu’s intense focus on obtaining 20 F-35 planes as a condition for agreeing to a 90-day freeze on settlements in the West Bank.

If Mr. Obama achieves a Middle East peace deal, veterans of Capitol Hill say, it would be such a momentous achievement that it would transcend politics. But first Mr. Obama has to get there, and even his allies worry that by getting bogged down in squabbles with Mr. Netanyahu, the president is risking his credibility and opening himself to partisan attacks.

“The administration needs to choose its confrontational points wisely, and win them,” said Robert Wexler, a former Democratic congressman from Florida who runs the S. Daniel Abraham Center for Middle East Peace, a nonprofit organization in Washington. “The president,” he added, “is not a warm-up act; he’s the closer.”