President Bush and Senator Kerry yesterday gave New Yorkers a preview of the presidential debates, with Mr. Kerry criticizing Mr. Bush for going to war in Iraq and Mr. Bush responding directly just hours later.

In a speech at New York University, Mr. Kerry yesterday gave the public a taste of his new campaign theme, describing the Iraq war as “a profound diversion” from the war on terror. “We have traded a dictator for a chaos that has left America less secure,” Mr. Kerry said.

Later, in remarks to a fund-raiser at the Sheraton New York, Mr. Bush noted that Mr. Kerry had voted for the war. “Today my opponent continued his pattern of twisting in the wind, with new contradictions of old positions,” Mr. Bush said. He quoted Mr. Kerry saying in December of 2003 that those who think America is not safer after having captured Saddam Hussein “don’t have the judgment to be president or the credibility to be elected president.”

“I couldn’t have put it better,” Mr. Bush said.

Mr. Bush is expected to speak about Iraq and the war on terrorism when he addresses the United Nations General Assembly today. The prime minister of Iraq, Iyad Allawi, will be here for the U.N. meeting and is also expected to meet separately with Mr. Bush.

Mr. Kerry’s comments apparently indicated a belief that Mr. Bush is vulnerable politically on the Iraq war – not only on his management of the war, but on the decision to go to war itself. During the Democratic primaries, Mr. Kerry and his running mate, Senator Edwards, were criticized by Governor Dean, Rep. Dennis Kucinich, and the Reverend Al Sharpton for voting in favor of the Iraq war. The shift by Mr. Kerry may be driven by the increase in Americans killed in Iraq, or by a campaign strategy of energizing the Democratic base of antiwar activists. Another factor, observers say, is the hope of winning voters away from third-party candidate Ralph Nader, who opposed the war in Iraq.

Whatever the reasons, Republicans emphasized yesterday that Mr. Kerry’s new stances on the war were indeed new.

“Flip flop flip flop flop flip flip,” said Mayor Giuliani, who spoke minutes before Mr. Bush at the Republican fundraiser. “We need a commander in chief who is consistent,” Mr. Giuliani said. “The security of the United States cannot be decided by putting your finger in the wind.”

“The president is for real. He’s straight,” Mr. Giuliani said, while Mr. Kerry is “someone who can’t figure out what position he is going to take today or tomorrow or the next day.”

Governor Pataki, who also spoke at the fund-raiser, said, “This afternoon John Kerry set a record. He had 14 flipflops.”

In his appearance at NYU, Mr. Kerry said America in Iraq is “fighting a growing insurgency in an ever-widening war zone.” He said Mr. Bush’s “two main rationales” for the war, “weapons of mass destruction and the Al Qaeda-September 11th connection, have both been proved false.” He blamed Mr. Bush for “colossal errors of judgment” and “outright incompetence.”

“If we do not change course, there is the prospect of a war with no end in sight,” Mr. Kerry said.

Mr. Kerry offered a four-point plan to “make a fresh start in Iraq.” He called for seeking greater international support, training Iraqi security forces, using more Iraqi contractors to rebuild Iraq, and recruiting international troops to protect U.N. workers organizing the January elections in Iraq.

In his appearance in New York and in a campaign appearance yesterday afternoon in Derry, N.H., Mr. Bush defended his decision to go to war in Iraq. “Knowing what I know today I would have made the same decision,” he said.

“It’s hard to imagine a candidate running for president who prefers the stability of a dictatorship to the hope and security of democracy,” Mr. Bush said.

“Saddam Hussein was a sworn enemy of America. He harbored terrorists,” Mr. Bush said. “Saddam Hussein paid the families of suicide bombers.”

Mr. Bush defended his economic record and said Mr. Kerry would raise taxes. “If we want the economy to grow, we’ve got to keep taxes low,” Mr. Bush said.

He accused Mr. Kerry of wanting “to nationalize health care,” and offered a veiled attack on Mr. Edwards, who made his fortune as a plaintiff’s lawyer. “We’ve got to stop these frivolous lawsuits that are running good docs out of business,” Mr. Bush said. “I don’t think you can be pro-doctor and pro-trial lawyer at the same time. I am for medical liability reform now.”

Mr. Bush’s remarks were interrupted several times by supporters chanting in Spanish, “Viva Bush.” Mr. Bush answered back in Spanish, “Vamos a ganar. Mis amigos latinos esta aqui.”

When he was interrupted in Spanish again, he said, “Only in New York. I love this city. What a great place, tremendous diversity.”

The Bush fund-raiser attracted a few hundred supporters who paid a minimum of $2,000 each to stand and eat hors d’oeuvres. A dinner with the president followed for donors at higher levels. The fund-raiser wasn’t for the Bush-Cheney campaign, but for the Republican National Committee, which is controlled by Mr. Bush. The chairman of the Conservative Party of New York, Mike Long, appeared at the event; Mr. Bush will appear on the Conservative Party line in addition to the Republican one on the New York ballot in November.

At two other events in Manhattan yesterday, Mr. Kerry focused on the theme of “two Americas” and the state of the economy. He called the November election the “most important election of our lifetime, bar none.”

At Redbook magazine’s annual “Mother and Shakers” awards luncheon at Lincoln Center, Mr. Kerry’s wife, Teresa Heinz Kerry, was honored by the magazine “for inspiring Americans to help others.” During the keynote address, Mr. Kerry described America as a nation beset by “deficits out of control, our relationships in the world tattered, the respect for the United States the lowest we’ve seen in years.”

“You ask yourselves whether we could do better,” Mr. Kerry said.

“Never has this nation been more divided than it is today,” Mr. Kerry told donors gathered at the New York Hilton later yesterday evening for a fund-raiser. “I intend to unite America into one country.”

Mrs. Kerry, who preceded her husband on the podium at each event, defended his new position on the Iraq war. “There’s a time for everything and it was time for him to take off the gloves,” Mrs. Kerry said at the fundraiser as her husband’s campaign theme song, U2’s “Beautiful Day,” began playing in the background. “He’s my rock star,” she said.

Also yesterday, the Republican and Democratic campaigns agreed on a schedule of debates that will exclude Mr. Nader. The debates are scheduled for September 30 in Coral Gables, Fla; October 8 in St. Louis, and October 13 in Tempe, Ariz. A debate between the Republican and Democratic candidates for vice president is set for October 5 in Cleveland.