A leading Republican congressman warned that the climate toward Israel on Capitol Hill could be changing, ahead of his address to a major Jewish conference Sunday.

"The possibility is there," US House of Representatives Minority Whip Eric Cantor told The Jerusalem Post, speaking about the prospect that Congress's support for Israel could be ebbing.

"There have been incidences of late that do indicate that we have challenges on that front, and I'm very committed to doing everything I can to make sure that Congress remains Israel's strongest ally in the quest for what it needs in terms of its security."

Cantor, who spoke to the Post before addressing the Jewish Federations of North America's annual General Assembly, did not specify the nature of the incidents, but he did raise questions about the White House's approach to Israel and the wider Middle East.

"I have a lot of concerns about what I have seen lately, about the continued desire to try to engage with Iran and about pressure being applied to Israel in terms of concessions in the name of peace," said Cantor, the No. 2 Republican in the House and its only Jewish Republican.

"Israel is a pillar in our national security strategy and we ought to be emphasizing every bit of our commitment to Israel right now as it faces an existential threat," he said.

Cantor later spoke at the opening session of the convention, which was meant to feature an address by US President Barack Obama on Tuesday. But Obama pulled out late Saturday to attend the planned memorial service for the 13 victims slain by gunman Nidal Malik Hassan at Fort Hood in Texas.

Conference organizers said White House Chief of Staff Rahm Emmanuel would address the gathering in Obama's place. A small group of Jewish leaders are also due to meet with Obama at the White House.

Though many of the 3,000 registered attendants expressed dismay that the president wouldn't be attending the event, they accepted his decision to travel to Fort Hood.

Several also expressed interest in hearing from Emmanuel, a key figure in the administration who has been intimately involved in crafting and executing much of Obama's agenda.

"There's a disappointment, but we clearly understand. It's unfortunate," said Michael Gelman, chairman of the executive board of the Jewish Federations.

"We may even get more from Rahm Emmanuel than from the president" in terms of policy specifics, Gelman added.

He expects that the crowd would be enthusiastic to hear Emmanuel, even if he had big shoes to fill, saying, "I think he'll be received very well. He's probably the No. 1 adviser to the president."

Others, though, pointed to reported tension between Emmanuel and the Netanyahu government, seeing the chief of staff as a key factor in the differences between the two countries.

"I think this is going to be a tough crowd for Rahm Emmanuel, who's rumored to be one of Israel's toughest critics within the White House," said one Washington Jewish leader at the conference. "There's a lot of pressure on Rahm Emmanuel at this event to explain how a nice Jewish boy became White House chief of staff and sends his kids to a Jewish school while advising his president on a speech in Cairo that put tremendous pressure on Israel."

At the same time, a long anticipated meeting between Obama and Prime Minister Binyamin Netanyahu, in town to address the GA on Monday, is scheduled to take place later that day, the White House confirmed late Sunday.

Netanyahu is also scheduled to meet with members of Congress before traveling on to France.

Netanyahu's spokesman Nir Hefetz said the prime minister was always happy to talk face-to-face with Obama, but was not concerned that no such conversation had been formally announced even as he was within hours of landing in the US.

This trip was planned independent of an expectation that such a meeting would occur, Hefetz told Israel Radio, in an interview he conducted on the plane.

"If the trip's objective had been to meet with the president of the United States, then such a meeting would have been secured in advance of the trip," Hefetz said. "The prime minister decided to travel to Washington to address the second largest Jewish community in the world after Israel, the American Jewish community."

He wanted to update them on Israel's diplomatic situation, including the fallout from the Goldstone Commission's report, which accused Israel of war crimes, and the growing threat from Iran.

Israeli officials are in daily contact with the White House and the State Department, said Hefetz. He added that Netanyahu held consultations with his advisers in his home until close to midnight on Saturday.

He noted that both Obama and Netanyahu were relatively new to their offices and that it took time to build a strong personal relationship. The wider relationship between Israel and the United States remains strong and is not dependent on one person or the other, Hefetz said.