In a prime-time speech on the opening night of the Republican National Convention, McCain heartily endorsed the Iraq and anti-terrorism policies of his 2000 rival for the White House.
"Our choice wasn't between a benign status quo and the bloodshed of war," McCain told delegates at New York's Madison Square Garden. "It was between war and a graver threat. Don't let anyone tell you otherwise. Not our critics abroad. Not our political opponents."
McCain joined another popular Republican politician, , in lauding Mr. Bush as a strong and decisive wartime leader.
"In choosing a president, we really don't choose a Republican or Democrat, a conservative or liberal," Giuliani said in prepared remarks that compared Mr. Bush with Ronald Reagan and Winston Churchill. "We choose a leader. And in times of danger, as we are now in, Americans should put leadership at the core of their decision."
Earlier, Republicans kicked off their four-day gathering at New York's Madison Square Garden by adopting a platform that endorses the president's agenda. Delegates also officially placed the names of Mr. Bush and Vice President Dick Cheney in nomination for a second term in the White House.
CBSNews.com webcast of the GOP convention.
Absent from McCain's remarks were any criticisms of Democratic presidential candidate Sen. John Kerry, a friend. He also omitted any references to the Vietnam War, which has become an issue in this year's campaign because of the contrast between Kerry's service there and Mr. Bush's time in the Texas National Guard at the height of the war.
McCain said the debate over Iraq and terrorism "should remain an argument among friends who share an unshaken belief in our great cause, and in the goodness of each other."
"I don't doubt the sincerity of my Democratic friends," McCain said. "And they should not doubt ours."
McCain said Mr. Bush has earned re-election because of his resolute actions since the terrorist attacks of Sept. 11, 2001.
"He has been tested and has risen to the most important challenge of our time, and I salute him," McCain said.
"I salute his determination to make this world a better, safer, freer place," McCain said. "He has not wavered. He has not flinched from the hard choices. He will not yield. And neither will we."
A prisoner of war for five years in Vietnam, McCain is also popular among veterans. They will be a key voting bloc in Mr. Bush's race against Kerry, who was wounded during his Navy service in Vietnam.
McCain said the American drive against terrorism is "the test of our generation" and, paraphrasing President Franklin D. Roosevelt, "our rendezvous with destiny."
While McCain's tone was mostly conciliatory, he criticized Michael Moore, whose documentary film "Fahrenheit 9-11" attacks Mr. Bush over Iraq and has been popular with liberal audiences. Without mentioning Moore by name, McCain called him "a disingenuous film maker who would have us believe that Saddam's Iraq was an oasis of peace."
As cameras panned to where Moore was seated in the arena, the crowd booed loudly and began to chant, "Four more years, four more years." Security personnel surrounded Moore and refused to let anyone in or out of his section.
Mr. Bush, meanwhile, campaigned in New Hampshire and triggered an instant campaign stir when he told an interviewer he doubted victory is possible in the war on terror.
"I don't think you can win it. But I think you can create the conditions that those who use terror as a tool are less acceptable in parts of the world," he told NBC.
Democratic vice presidential candidate John Edwards quickly labeled that a concession of defeat in the war that terrorists launched in 2001.
"This is no time to declare defeat — it won't be easy and it won't be quick, but we have a comprehensive long-term plan to make America safer," he said of the Kerry campaign. "And that's a difference."
White House spokesman Scott McClellan hastened to clarify the president's remarks.
"He was talking about winning it in the conventional sense ... about how this is a different kind of war and we face an unconventional enemy," said the president's spokesman. "I don't think you can expect that there will ever be a formal surrender or a treaty signed like we have in wars past."
The convention began with polls showing the president and Kerry in a virtual tie. The first day was intended to focus on Mr. Bush's leadership in the war on terrorism, with a tribute to families of the Sept. 11 attacks.
Republicans roared voice-vote approval of a party platform that rallies behind Mr. Bush's agenda while endorsing positions dear to conservatives, including backing constitutional bans on gay marriage and abortion.
"Our platform highlights the principles that unite our party," Senate Majority Leader Bill Frist, the platform chairman, told delegates.
Republicans convened about four miles north of Ground Zero, where two hijacked planes destroyed both towers of the World Trade Center. Nearly 3,000 people died there, at the Pentagon and at a crash site in Pennsylvania.
Thousands of police kept the city under tight security as the convention opened. Normally bustling Penn Station was all but empty of travelers, with police officers posted every few feet.
Protesters, who numbered at least 120,000 during loud but peaceful demonstrations on Sunday, generally gave back the streets of Manhattan to commuters. One group of protesters in oversize Mr. Bush masks and wild costumes heckled convention-goers as they left their hotels Monday morning.