With early voting set to begin this morning in Florida, Senator Kerry of Massachusetts kicked off a two-day campaign swing through the retireerich battleground state by warning senior citizens that President Bush is hatching a secret plan to privatize the Social Security program.

“I’ll tell you what, I will never privatize Social Security. I’ll never cut the benefits and I won’t raise the retirement age,” Mr. Kerry vowed during an afternoon rally in Pembroke Pines, Fla.

Earlier in the day, in Ohio, the Democratic nominee accused Mr. Bush of planning a post-election surprise on Social Security that he is unwilling to discuss in public.

“This may be a good surprise for the wealthiest people and the well-connected in America, but it’s a disaster for America’s middle class,” Mr. Kerry said.

The Kerry campaign also unveiled a new television ad that says Mr. Bush’s plans for Social Security could result in benefit cuts of 30% to 45%.

The barrage of criticism from Mr. Kerry and his campaign was intended to capitalize on a news report that Mr. Bush recently told top GOP fund-raisers that if he is re-elected he plans to make a full-court press for dramatic changes in Social Security.

According to an article in yesterday’s New York Times Magazine, Mr. Bush told the donors: “I’m going to come out strong after my swearing in … with fundamental tax reform, tort reform, privatizing of Social Security.” The writer of the story did not attend the event where Mr. Bush purportedly made the remark. The author, Ronald Suskind, wrote that he cobbled together that quote and others from the recollections of “several guests at the lunch,” as well as notes he obtained about the gathering.

A spokesman for Mr. Bush’s campaign, Kevin Madden, denied Mr. Bush ever made such a comment.

“The president has never used the word privatization,” Mr. Madden said. “The Kerry campaign is taking third hand, made-up quotes to scare seniors.”

The attack over Social Security appeared to catch the Bush campaign somewhat flat-footed. It came on a day that advisers to Mr. Bush described as his last day off before the election. The president appeared before cameras only briefly and at a distance, as he came and went from church in the capital.

As a result, the response to the Kerry campaign’s onslaught was left to others. On NBC’s “Meet the Press,” Mr. Bush’s campaign manager, Kenneth Mehlman, defended the president’s reform plans but did not explicitly deny the purported quote about privatization, which appeared several days ago in advance editions of the Times magazine.

“If you do nothing, which is what John Kerry wants to do, it costs $10 trillion,” Mr. Mehlman said on NBC. He said Mr. Bush favors allowing younger workers to set up personal retirement accounts with part of their payroll tax.

The Bush campaign later issued a statement saying the president had been misquoted. The Republican Party also struck back with a fact sheet about Mr. Suskind, which noted that he is a registered Democrat and pointed out allegations that a piece he wrote about the Boston Celtics basketball team nearly a decade ago was inaccurate and libelous.

Mr. Suskind did not return a call seeking comment for this story.

Neither Mr. Kerry nor his campaign advisers said precisely what aspect of Mr. Bush’s alleged comments they view as a surprise. The president has spoken repeatedly about his desire to make changes in Social Security to help accommodate demographic stresses on the program caused by the retirement of large numbers of baby boomers. He usually speaks, however, about “personal accounts,” not private accounts or privatization.

In the press and in discussions about reform, those terms are often used interchangeably, but pollsters say “privatization” makes many senior citizens skittish. The Kerry campaign also appeared to imply that Mr. Bush might favor broader changes to the entitlement program.

A senior adviser to Mr. Kerry, Tad Devine, made clear yesterday that the sudden focus on Social Security was intended to turn older voters in Florida against Mr. Bush.

“He’s in trouble,” Mr. Devine said in a conference call with reporters. “He’s now said something on the record which, unfortunately for him, I think the voters from that state will wholeheartedly reject. … I think it’s going to hurt him very badly with voters from Florida and elsewhere.”

New polls continued to paint an uncertain picture of the presidential race. A CNN/USA Today/Gallup poll found Mr. Bush with a clear lead among likely voters. In that survey, the president had 52% support while Mr. Kerry had 44%. Several other polls released over the weekend showed either a tie or a small advantage for Mr. Bush. An average of six recent national polls showed Mr. Bush leading by four percentage points.

Democrats said they were not very concerned by the numbers. They noted that the Gallup Poll, in particular, has oscillated wildly in recent weeks. At one point Mr. Bush appeared to have a lead of 13 percentage points, but a short time later Mr. Kerry was ahead by a point.

A Democratic pollster, Stanley Greenberg, released a survey that showed Mr. Kerry leading the president by three percentage points among likely voters, with 50% supporting the senator and 47% in favor of Mr. Bush. Mr. Greenberg’s poll used a methodology that allows newly registered voters to be counted as likely voters. Most polls sponsored by news organizations do not.

In Washington yesterday, Mr. Kerry’s wife, Teresa Heinz Kerry, spoke to a Jewish women’s group about her philanthropic activities. In her remarks to a conference sponsored by the Lion of Judah of the United Jewish Communities, Mrs. Heinz Kerry highlighted work that she and her husband did on behalf of dissidents in the Soviet Union.

“There is a wonderful saying from the Talmud that I think perfectly captures the tension of our own times: ‘If I am not for myself, who will be for me? And if I am only for myself, what am I? And if not now, when?'” she said.

The first lady, Laura Bush, is to speak to the group today.

Meanwhile, Democrats made an effort yesterday to air complaints about the Bush campaign’s tactics toward people it suspects of planning to disrupt campaign events.

A high-school student from Iowa, John Sachs, 18, told reporters his life was threatened at a question-and-answer session Mr. Bush attended October 4 near Des Moines.

Speaking on a conference call organized by the Democratic Party, Mr. Sachs said a button he was wearing, which read, “Bush-Cheney ’04: Leave No Billionaire Behind,” was confiscated by a campaign worker. The student said he hoped to ask Mr. Bush about a possible draft, the war in Iraq, or entitlement programs, but an event organizer told him not to ask any questions, adding, “If you protest, it won’t be me taking you out, it will be a sniper.”

“It scared me,” Mr. Sachs said.

A spokesman for the Bush/Cheney campaign in Iowa, Daniel Ronayne, dismissed the allegation. “It’s preposterous,” he said.

Republican officials, too, have complained of intimidation of their staff and volunteers by groups affiliated with the Democratic Party.

The chairman of the Bush campaign, Marc Racicot, complained in a letter to the AFL-CIO last week that union-directed protests at GOP campaign offices “have led to injuries, property damage, vandalism and voter intimidation.”

A spokeswoman for the union denied involvement with the most serious incidents and said one confrontation stemmed from “confusion” that arose as union workers tried to deliver petitions to the Republican offices.