WASHINGTON — As the Republican presidential primary becomes increasingly combative, the four leading candidates will gather tomorrow in Washington to address the Republican Jewish Coalition in a forum that will likely center on national security and Middle East policy.

Organizers of the day-long event have been told to expect major foreign policy speeches from at least two of the Republican hopefuls, who have spent the last week sniping at each other over taxes, presidential decision-making, and party loyalty.

A spokesman for Mitt Romney said the former Massachusetts governor would use the forum to discuss his intention to stop Iran from acquiring nuclear weapons and to confront global terrorism, including offering specifics about his plans to increase the American military by 100,000 troops and strengthen government intelligence services. Tomorrow’s speech follows the release last week of a television advertisement titled “Jihad,” in which Mr. Romney says he would “monitor the calls Al Qaeda makes into America,” a reference to his support for the Bush administration’s domestic wiretapping program. There were signs that other candidates viewed tomorrow’s event as important. Fred Thompson was personally rewriting his speech yesterday, a spokeswoman said. She said the former Tennessee senator often takes his own pen to major addresses, and that he has surprised his own staff on occasion by inserting new policy ideas, such as when he added a proposal to index Social Security benefits to inflation at an economic summit earlier this month.

Mayor Giuliani, Senator McCain of Arizona, and Senator Brownback of Kansas are also scheduled to address more than 500 coalition members tomorrow.

On the issues most critical to the Republican Jewish community, the party’s top contenders are in broad agreement, the coalition’s executive director, Matthew Brooks, said.

“They are all very, very strongly supportive of Israel, and they understand the threats we face and our allies face from radical Islam,” Mr. Brooks said.

The candidates have been unequivocal in vowing to prevent Iran from acquiring nuclear weapons, including using military force if necessary. But Mr. Romney in particular may face the most pressure on this issue following his widely criticized response to a question in last week’s Republican debate about whether he would seek congressional authorization before ordering a strike on Iran’s nuclear facilities. “You sit down with your attorneys,” he said.

Rival campaigns quickly jumped on the remark and used it to highlight their own willingness to take decisive military action to prevent Iran from acquiring nuclear weapons. They also have been eager to keep the issue alive. In an appearance yesterday on CBS’s “Face the Nation,” Mr. McCain went out of his way to take a shot at Mr. Romney, answering an unrelated question on Iran’s nuclear capability to say, “I emphasize again, that’s not the time to call in the lawyers, as Governor Romney stated.”

Mr. McCain’s appearance may be scrutinized as well tomorrow, coming two weeks after he drew criticism from some Jewish leaders for saying in an interview that the Constitution established America “as a Christian nation.” He subsequently clarified his statement, and whether he will do so again before the RJC is unclear. “I think we’re beyond it,” Mr. Brooks said, adding that Mr. McCain had a long record of support from the Jewish community.

What could be expected from the Arizona senator are more digs at his opponents, as the speech follows a weekend in which he leveled his harshest criticism of Mr. Romney to date. In an address Saturday and again on “Face the Nation” yesterday, the Arizona senator assailed Mr. Romney for suggesting that he was the only “real Republican” in the race.

Mr. McCain brought up Mr. Romney’s past record, saying in New Hampshire on Saturday that when he was supporting Democratic candidates or taking “liberal” positions on abortion and other issues, “I don’t think he was speaking for Republicans.”

Mr. McCain added yesterday that Mr. Romney had changed his position on “literally every major issue” of the day.

“I think we owe the voters our respect before we get their respect,” he said on CBS. “And that respect means being straightforward on your record, run on your record, and justify the positions that you took.”

A spokesman for Mr. Romney, Kevin Madden, responded aggressively, issuing a statement that criticized Mr. McCain’s “wrongheaded” approach to immigration, his sponsorship of a campaign finance law that “stifled free speech,” and his opposition to President Bush’s tax cuts. “We will talk about these differences in a substantive way, rather than resort to the flailing attacks the senator is currently engaging in as a result of being without any new ideas to save his campaign,” Mr. Madden said.

Following the near collapse of his campaign over the summer, Mr. McCain is pinning his hopes almost exclusively on New Hampshire, the site of his lone primary win in 2000. His standing in the polls has risen, but his decision to go on the offensive reflects his need to prevent Messrs. Romney and Giuliani from pulling away from the field. To that end, Mr. McCain has joined Mr. Romney in criticizing the former New York mayor for helping to derail the presidential line-item veto during the 1990s.