Republicans kick off their convention here today with a determined effort to use the city’s first-hand experience with terrorism to bolster President Bush’s image as a resolute and unwavering leader of a country still under grave threat.

“A Nation of Courage” is the official theme for this first day of the GOP convention and New Yorkers are to assume key roles in conveying that message. Mayor Bloomberg is scheduled to be one of the first to address the delegates this morning at Madison Square Garden. Mayor Giuliani is to deliver the last speech of the day, during a late evening slot.

Senator McCain of Arizona will also deliver a prime-time address, paying tribute to America’s armed forces and to Mr. Bush for his actions as commander in chief.

At a rally on Ellis Island yesterday, several prominent Republicans, including Vice President Cheney, signaled that national security will be the convention’s predominant theme.

“All of us are here for one reason and one reason only and that is to make certain that George W. Bush is president for the next four years,” Mr. Cheney said. “He is exactly the leader we need for these times.”

Political image makers designed yesterday’s event so that cameras would capture lower Manhattan and the absent World Trade Center towers in the background as Mr. Cheney arrived at the island by boat and later as he addressed the crowd.

Most of the speakers, who included Governor Pataki and Mr. Giuliani, also made explicit reference to the terrorist strikes. The vice president did so as he stressed that fighting the war on terrorism remains the highest priority for the nation and Mr. Bush.

“A sure reminder of that is the skyline of this great city, which was altered so violently on September 11, 2001,” Mr. Cheney said during his subdued seven-minute speech. “There are those in this world who have set themselves against the freedoms we enjoy, fanatics who hate the idea of equality, who want everyone to live the way they do and who are willing to murder innocents to accomplish their goals. They’ve attacked our nation and they wish to do us further harm and it is for them and from them that we must protect our children, our country, and our future.”

Speaking from the same podium, Mayor Giuliani said he hoped that the convention would help Mr. Bush and Mr. Cheney recapture the goodwill they enjoyed in the days following the terrorist attacks.

“We also can’t stand here without looking behind us and seeing the skyline of the greatest city in the world, missing something that meant so much to us, those two towers and all those people that we lost,” Mr. Giuliani said. “So throughout this week, as all Americans, we’ll remember them and we’ll remember the support that President Bush and Vice President Cheney gave us through those terrible and difficult days.”

In an exchange with reporters later, Mr. Giuliani credited Mr. Bush for being unafraid to use the American military to confront the terrorists overseas.

“We have to be on the offense against terrorism if we’re going to give ourselves the best chance of avoiding another attack,” Mr. Giuliani said.

In his speech tonight, Mr. Giuliani plans to compare Mr. Bush to other leaders who have shown unusual prescience in the fight against evil.

“Winston Churchill saw the dangers of Hitler when his opponents and much of the press characterized him as a war mongering gadfly. Ronald Reagan saw and described the Soviet Union as ‘the evil empire’ when world opinion accepted it as inevitable and belittled Ronald Reagan’s intelligence. George W. Bush sees world terrorism for the evil that it is and he will remain consistent to the purpose of defeating it while working to make us ever safer at home,” Mr. Giuliani will say, according to excerpts of his speech released to the press late yesterday.

Mr. McCain will strike a similar chord in his address to the delegates. According to convention planners, the senator and Vietnam War veteran plans to say of Mr. Bush, “He has been tested and has risen to the most important challenge of our time, and I salute him…He has not wavered. He has not flinched from the hard choices. He will not yield. And neither will we.”

Political analysts said the intense focus on national security was part of the party’s decision to stage the convention in New York.

“The only reason to be here is to exploit 9/11, is if this is Bush’s crowning achievement, which pretty much is what the campaign is saying,” said Chuck Todd, editor in chief of a popular political newsletter, the Hotline.

Later this week, convention speakers are scheduled to address issues such as the economy and Mr. Bush’s commitment to exporting democracy. Those speakers are also expected to make mention of the war on terror in some fashion.

While moderates seem to have won most of the high-profile speaking slots, Mr. Giuliani insisted yesterday that a wide range of views would be showcased. “The speeches at our convention are going to span the length and breadth of the Republican Party, not like the Democratic Party where there was very, very scripted speeches,” he said.

Mr. Bloomberg did not attend yesterday’s rally at Ellis Island. At that hour, he was hosting an event at Gracie Mansion for the Congressional Hispanic Caucus.

In an interview with Time Magazine, Mr. Bloomberg suggested that Mr. Bush should be careful as he attempts to harness the emotions of September 11 to boost his re-election bid. Asked if Mr. Bush should go to ground zero, the mayor said, “I think that at this point it has become so politicized that he would be criticized more for going than not going. It’s a shame that it’s gotten down to that, because normally I would give you an answer, ‘Everybody should be able to go every place.’ “

Mr. Cheney showed no reticence yesterday about invoking September 11-related imagery. He called attention to Mr. Bush’s visit to firefighters at ground zero three days after the attacks.

In March, Mr. Bush faced criticism from Democrats and some families of victims after his campaign released ads that included images from the devastated World Trade Center. Some critics noted that he once said he had no desire to use the event for political purposes. The new invocations of September 11 could rekindle those attacks.

“I don’t think it’s subtle anymore. There used to be some subtlety to it,” Mr. Todd said. “Why doesn’t he just deliver the speech with the bullhorn? That’s about the only thing at this point that would be over the top.”