WASHINGTON – Senator Kerry took of the gloves yesterday, directly criticizing President Bush for attacking his military record in Vietnam through a surrogate group that has questioned the Massachusetts lawmaker’s service in a war in which he won five medals.

Speaking before the annual convention of the International Association of Fire Fighters in Boston, Mr. Kerry for the first time tied Mr. Bush’s re-election campaign to the Swift Boat Veterans for Truth.

“The fact that the president won’t denounce what they’re up to tells you everything you need to know, he wants them to do his dirty work,” he said.

The group’s ads feature testimonials from veterans who claim to have served with Mr. Kerry in Vietnam and argue he has lied about his record for political gain.

In one advertisement, the group takes issue with Mr. Kerry’s Bronze Star medal, claiming that he did not rescue crewmates under enemy fire as the senator has claimed in subsequent interviews.

The Democratic Party made its candidate’s record in Vietnam a centerpiece of the presidential campaign. Last month, Mr. Kerry’s acceptance speech in Boston was previewed with home movies and photographs of his days as a soldier. He began his remarks with a salute, saying he was “reporting for duty.”

A spokesman for the Bush campaign told The New York Sun yesterday that Mr. Kerry knew the charge that Mr. Bush was using the Swift Boat veteran ads indirectly was false.

“Senator Kerry knows that President Bush has called his service in Vietnam noble,” Kevin Madden said. “The president has called for the end to all of the unregulated soft-money activity.”

Nonetheless, neither the president nor Mr. Madden would specifically disassociate the campaign from the advertisements from the Swift Boat Veterans for Truth, who received $200,000 this year from a Bush financial supporter from Texas, Robert Perry. Mr. Perry contributed to Mr. Bush’s campaign for governor in Texas and his first run for the White House in 2000.

Mr. Kerry has also benefited from independent groups funded by unregulated soft money that attack his opponents under organizations governed by section 527 of the tax code. These groups, called 527s, like Moveon.org, have also attacked the president’s record.

Moveon.org, for example, claimed the president lied about knowing there were weapons of mass destruction in Iraq. While Mr. Kerry has pledged that he would not bring up the president’s years in the Air National Guard during the Vietnam War, other prominent Democrats, like retired General Wesley Clark, have.

“The whole problem of the section 527 groups is they can come off appearing to be independent, and then do the dirty work for the campaigns,” said a campaign finance lobbyist for Public Citizen, Craig Holman. “The candidates can then criticize and pretend to be above the controversy. They are working in tandem with the campaigns. They are part and parcel of the campaigns. The candidates criticize the mud-throwers as if they have nothing to do with it.”

The executive director of the Center for Public Integrity, Charles Lewis echoed Mr. Holman’s remarks. “Both candidates are cute about these outside expenditures,” he said. “But Bush doesn’t exactly have a stellar history, going back to his father and Willie Horton. Republicans and particularly his family are not novices about independent groups operating outside of the campaign.”

Mr. Lewis said he was disappointed in Mr. Kerry and the president for their use of outside groups in this election season. He noted that Mr. Bush’s track record was particularly relevant because Bush supporters in South Carolina in the 2000 Republican primary ran ads attacking Senator McCain, a Republican from Arizona, alleging he had an illegitimate biracial daughter.

Mr. McCain has called on the president to denounce the Swift Boat ads. His office had no comment yesterday.

The director of the Annenberg Public Policy Center at the University of Pennsylvania, Kathleen Hall Jamieson said one reason why Mr. Kerry attacked the president over the use of the Swift Boat ads is because of a Washington Post investigation into the claims in the ad.

The story, published yesterday, disclosed that the military records of Larry Thurlow , the veteran who claimed Mr. Kerry’s boat was not under fire in the incident for which he received the Bronze Star, contradict the political ad.

Mr. Thurlow for his part issued a statement yesterday standing by his account that Mr. Kerry’s boat was not under enemy fire. He said the record attributed to Mr. Thurlow was taken from language from Mr. Kerry’s report of the incident.

“To this day, I can say without a doubt in my mind, along with other accounts from my shipmates – there was no hostile enemy fire directed at my boat or at any of the five boats operating on the river that day,” the statement said.

Ms. Jamieson said she could understand how memories of the incident could differ after so many years, but she said it appears Mr. Kerry’s account of his record in Vietnam looked more accurate than the Swift Boat Veterans for Truth.

“We are beginning to put together a case that the record confirms Kerry’s side,” she said. “A reasonable inference is that none of this has to do with what Kerry did in Vietnam, it all has to do with what he did when he protested the war at home.”

When Mr. Kerry arrived home after the war, he joined a veterans group opposed to the conflict. At one point, he testified before Congress that American soldiers were committing war crimes in Vietnam.

The controversy over Mr. Kerry’s service in Vietnam may soon subside. This weekend another Republican, Senator Warner, the Virginia lawmaker who heads the Armed Services Committee, said he did not regret his decision to award Mr. Kerry medals when he was the undersecretary and secretary of the Navy under President Nixon.