Connecticut Attorney General Richard Blumenthal (D) was alternately apologetic and defiant Tuesday as he battled to deflect a potentially devastating blow to his Senate campaign: an accusation that he had exaggerated his military service record.

Blumenthal, his party's presumptive nominee in the contest to succeed retiring Sen. Christopher J. Dodd (D), held a news conference in West Hartford to respond to the New York Times report Monday night that he has lied about serving in Vietnam.

"On a few occasions I have misspoken about my service, and I regret that and I take full responsibility," Blumenthal said, flanked by veterans. "But I will not allow anyone to take a few misplaced words and impugn my record of service to our country."

Blumenthal joined the Marine Corps Reserves in 1970 and served six years, all in the United States. He has accurately described his service many times in his career, but in 2008, he told an audience at an event in Norwalk: "We have learned something important since the days that I served in Vietnam. And you exemplify it. Whatever we think about the war, whatever we call it -- Afghanistan or Iraq -- we owe our military men and women unconditional support."

Blumenthal explained Tuesday that he meant to say he served "during" Vietnam, not "in" Vietnam. And he stressed that "there were no special favors, no privileges involved" in his securing a slot in the Marine Reserves.

The Times article about Blumenthal's military record noted that he received five draft deferments before his enlistment, including one during which he served as an assistant to then-Washington Post Publisher Katharine Graham.

The controversy could place Connecticut's contest among the most competitive Senate races in November. Blumenthal had been heavily favored to win since January, when he plunged into the race after Dodd announced that he would end his foundering reelection bid. Former World Wrestling Entertainment executive Linda McMahon and former U.S. representative Rob Simmons are competing for the Republican nomination.

Stuart Rothenberg, author of the nonpartisan Rothenberg Political Report, said Blumenthal's revelation instantly made the race "significantly more competitive."

"He's got a terrible credibility problem here, and I think what makes it so dramatic is this is a guy who had such a squeaky-clean reputation," Rothenberg said.

Both Republican candidates pounced on the opportunity to attack Blumenthal.

"The report clearly raises some very serious questions -- questions that cannot be dismissed and aren't easily answered," said McMahon spokesman Ed Patru.

There was no sign Tuesday that any national Democrats were abandoning Blumenthal, and Democrats' initial defense was to attempt to turn the story around on McMahon by accusing her of peddling negative information.

Simmons, meanwhile, is in a position to attack Blumenthal from a different angle: He is a decorated Vietnam veteran.

"As someone who served, I respect Richard Blumenthal for wearing the uniform, but I am deeply troubled by allegations that he has misrepresented his service," Simmons said in a statement Monday.

An independent poll of the GOP contest taken in March showed McMahon with a 10-point lead over Simmons. Aided by her vast personal wealth, McMahon has also been able to outspend Simmons.

Democrats breathed a sigh of relief when Dodd announced that he would retire after 30 years in the Senate; polls had shown him trailing both Republican candidates. Blumenthal stepped in with high approval ratings, bolstered over his two decades as attorney general by his high-profile crusades against corporate interests. But he has not run in a competitive race for many years and so has avoided the scrutiny such campaigns can bring.