Maryland Democratic Rep. Roy P. Dyson, rocked by revelations about his Vietnam draft status and ties to defense consultants, lost his bid for a sixth term yesterday to Republican challenger Wayne T. Gilchrest.

Gilchrest, 44, a schoolteacher who made integrity his main campaign theme, won 56 percent of the vote and carried 10 of the district's 13 counties, including two in Dyson's home base in Southern Maryland.

The winner appeared to have benefited from an eleventh-hour blitz of television ads and a campaign appearance by Vice President Quayle.

In a gracious five-minute concession speech to about 150 supporters at the Fager's Island Hotel in Ocean City, Dyson said, "Don't worry about what happened tonight . . . I can add, and the numbers don't look good."

"God bless Wayne Gilchrest. He needs it," Dyson said to a smattering of boos from the crowd. "We are going to help him, we really are, because what is important is this district. It's more important than me."

At the winner's rally, Gilchrest took note of Dyson's conciliatory remarks, calling them "a fine way to leave the race." But in a caustic reference to the appearance of Dyson's mother, Marie, in a campaign commercial, Gilchrest added, "Mrs. Dyson, you now have your son back."

As their new congressman, Gilchrest said the people of the 1st District "can expect to have a personal . . . intellectual and . . . moral commitment" from him.

The race, a rematch of the contest two years ago that Dyson narrowly won, drew national interest because of the incumbent's perceived vulnerability. In addition to Quayle, four Bush administration Cabinet secretaries traveled to Maryland's 1st Congressional District on Gilchrest's behalf.

It was the only congressional race among the eight in Maryland in which the incumbent even faced a close challenge. Voters easily returned the seven other House members, including Republican Rep. Constance A. Morella of Montgomery County and Democratic Rep. Steny H. Hoyer of Prince George's.

Democratic Rep. Beverly B. Byron, whose district includes upper Montgomery County and Western Maryland, also won reelection, as did Democratic Reps. Tom McMillen and Benjamin L. Cardin.

At Gilchrest's celebration at an American Legion post near his Kent County home, former state Republican Party chairman Allan Levey said, "This race had nothing to do with the {national} trend toward throwing the incumbents out."

Referring to revelations about Dyson's campaign contributions and his record in office, Levey said, "What was hanging over Dyson's head two years ago is still hanging."

Gilchrest spokesman Tony Caliguiri said the challenger benefited in part from Dyson's use of strong negative ads near the end of the campaign.

Dyson "got out the heavy artillery. Unfortunately I think he shot himself in the foot," Caliguiri said.

Dyson, 42, was first elected in 1980 after a sex and alcohol scandal enfeebled Republican veteran Robert Bauman, an arch conservative who had continued the GOP's traditional dominance of the conservative district. Two years ago, Dyson himself came under a cloud after his chief aide, Thomas M. Pappas, committed suicide in the wake of news stories questioning his management of Dyson's office and campaign funds.

Further disclosures linked Dyson, a top recipient nationally of political action committee contributions, to a circle of defense industry consultants who eventually were convicted in a federal criminal probe of Pentagon procurement practices.

Gilchrest's victory increased the GOP's representation in the state's congressional delegation from two to three.

After his narrow 1,540-vote victory over Gilchrest in 1988, Dyson began his reelection campaign almost immediately.

He arranged congressional hearings in the district, blanketed its 13 counties with federally funded mail and raised an estimated $600,000 to retire debts from the 1988 race and finance his rematch with the Kent County schoolteacher. The district includes Southern Maryland, the Eastern Shore and part of Harford County north of Baltimore, and Dyson tried to maintain a presence in every farm and fishing village.

Not all went smoothly, however. Two weeks before the primary, it was revealed he was a conscientious objector during the Vietnam War, a fact that contrasted with his pro-defense posture on the House Armed Services Committee and receipt of tens of thousands of dollars from defense industry political action committees.

Gilchrest, meanwhile, a Marine combat veteran, made honesty and integrity the centerpiece of his campaign.

"Who do you believe?" asked one Gilchrest ad. "Roy Dyson? Or veteran, teacher, family man Wayne Gilchrest?"

In an attempt to stay on the offensive, Dyson attacked Gilchrest as too liberal on issues such as the environment and gun control, which are important on the Eastern Shore, and blasted Gilchrest's support for a Medicare premium increase to help balance the budget.

Gilchrest, however, addressed those criticisms head-on, visiting waterfront communities, for example, to explain his stance on wetlands regulations and condemning Dyson's opposition to every proposal in the recent federal budget debate.

Staff writer Paul Duggan and special correspondent Todd Spangler contributed to this report.