NEW YORK — More than 100,000 demonstrators marched past a heavily fortified Republican convention hall on Sunday, chanting denunciations of the Bush administration and the war in Iraq as delegates flocked to the city to nominate President Bush for four more years in the White House.

Vice President Dick Cheney campaigned his way into the convention city three days ahead of the president, praising him as “calm in a crisis, comfortable with responsibility and determined to do everything needed to protect our people.” He spoke on Ellis Island, framed by a Manhattan skyline altered irrevocably by terrorism.

Bush was in West Virginia, a state he won four years ago and is laboring to carry again. Locked in a tight race with Democratic Sen. John Kerry, the Republican is scheduled to arrive in New York on Wednesday and deliver his formal acceptance speech the following night.

In an interview with Time Magazine, the president suggested he had underestimated the struggle of the postwar period in Iraq. “Had we to do it over again, we would look at the consequences of catastrophic success, being so successful so fast that an enemy that should have surrendered or been done in escaped and lived to fight another day,” Bush said.

Vice presidential candidate John Edwards responded for Kerry the Democrats. “President Bush now says his Iraq policy is a catastrophic success. He’s half right. It was catastrophic to rush to war without a plan to win the peace,” he said.

Polls show the war in Iraq has become increasingly unpopular in recent months, and the throng of protesters filling 20 city blocks on a steamy Manhattan afternoon underscored that. “No More Bush,” and “No More Years,” were two of the more popular chants. “Bush Lies, Who Dies?,” read some of the signs.

A small fire erupted along the protest route a half block from Madison Square Garden. Police doused the flames, then handcuffed two people and led them away.

Thousands of police, some dressed in riot gear, others bearing automatic weapons, watched as the protesters passed. Extensive as it was, the force represented only a portion of an unprecedented security force for the convention.

Homeland Security Secretary Tom Ridge said last week that the efforts would include air surveillance over the city, monitoring activity in the harbor and stationing security personnel at every hotel housing any of the 2,508 delegates or 2,344 alternates.

After months of appealing to his conservative supporters, Bush and his convention planners scripted a program pitched toward the political middle, independents and wavering Democrats. Sen. John McCain was on the program for the convention’s opening night Monday. The Arizona Republican has widespread appeal among independents that stems in part from his own presidential campaign four years ago and his drive for campaign finance reform.

California Gov. Arnold Schwarzenegger, who espouses a more moderate brand of Republicanism than the president, speaks Tuesday night. Democratic Sen. Zell Miller of Georgia delivers the keynote address on Wednesday.

Several speakers, McCain and former New York City Mayor Rudolph Giuliani among them, oppose the constitutional amendment to ban same-sex marriages that Bush has made a centerpiece of his campaign and is prominent in the Republican platform.

Cheney speaks Wednesday and Bush addresses the delegates and a nationwide television audience on Thursday. Aides have said he will use the speech to lay out an agenda for a second term.

Republican officials also say they intend to use the four-day convention to build support for Bush’s handling of the war on terror and the war in Iraq as well as to undermine Kerry’s claim as a suitable replacement.