Senator McCain’s swing through New York last night, which included an appearance on the “Late Show With David Letterman” and an event with Governor Pataki at his side, seemed clearly designed to blunt the momentum of his leading Republican opponent, Mayor Giuliani.

Mr. McCain — who told Mr. Letterman that he’d make his candidacy for president official in April — called Mr. Giuliani an “American hero,” but said he would “campaign hard” to get the Republican Party nomination.

The whirlwind visit to Mr. Giuliani’s hometown comes at a crucial crossroads for Mr. McCain. Two recent polls show that the mayor has widened his lead over the Arizona senator by as much as 23 percentage points among Republicans.

Even as he praised his opponent, Mr. McCain seemingly held on to the notion that momentum in politics can shift from week to week or day to day.

“The campaign is just beginning, but certainly I view Mayor Giuliani as an American hero and I can see why he’s very popular with many Americans,” Mr. McCain said after speaking at an event for the Irish-American Republicans in Midtown. “I feel that polls are polls and I think it’s probably accurate.”

He predicted a “spirited race” and said the GOP would have “some very good candidates to choose from.”

The positive tone marks a strong contrast to the recent campaign barbs exchanged between Senators Clinton and Obama, the leading candidates in the Democratic field.

The surprise appearance of Mr. Pataki, a political rival and colleague of Mr. Giuliani’s, was an interesting twist to Mr. McCain’s New York visit. Messrs. McCain and Pataki had a strained relationship after the governor backed President Bush in 2000 and attempted to knock Mr. McCain off the New York ballot. Both contended last night that they had mended the wounds years ago.

Mr. Pataki, whose own hopes to run for the Republican nomination were met with a lackluster response that led him to stop campaigning, said it was too early in the campaign season to decide on endorsing a candidate.

He praised Mr. McCain as a “true patriot,” but when asked whether he would appear with Mr. Giuliani or the other GOP candidates he said he would “be delighted to.”

Mr. McCain, who started his speech at last night’s event with an Irish joke, said he would not reverse any of Mr. Bush’s tax cuts and said he saw a window in the next few months for movement on immigration reform.

Meanwhile, Mr. McCain also announced an endorsement from a former Homeland Security Secretary and governor of Pennsylvania, Tom Ridge, and released the names of a 70-member finance team.

The list includes bigwigs such as a one-time owner of the Seattle Mariners, George Argyros, the CEO of Cisco, John Chambers, and Governor’s Schwarzenegger’s chief fund-raiser, Marty Wilson.

Mr. Argyros, one of Mr. McCain’s national finance chairmen, was one of the people Mr. Giuliani was hoping to tap for his fund-raising operation. According to a 140-page campaign blueprint that the Daily News obtained in January, Mr. Giuliani was planning to ask Mr. Argyros to be his Los Angeles finance chairman before he was snatched away.

“You’ve got heavy Orange County, which is sort of the goldmine for Republicans coming to California,” a California Republican analyst, Allan Hoffenblum, said of Mr. McCain’s team. “Orange County is to the Republicans what Hollywood and the West Side of Los Angeles is to the Democrats.”

Still, he said: “It is not difficult for two or three front-runners to cherry pick very nicely in California.”

Mr. McCain also was scheduled to appear at the New York Mercantile Exchange in Lower Manhattan, across the street from the World Trade Center site, where Mr. Giuliani surged to national prominence, but his campaign canceled the event because of travel delays. The Democratic National Committee seized on Mr. McCain’s visit to New York to criticize him for not being in Washington for votes in the Senate on 9/11 commission recommendations.