Rep. Roy P. Dyson (D-Md.) was criticized yesterday after the revelation that the pro-defense congressman was a conscientious objector during the Vietnam War, a designation given sparingly in Dyson's home county in Southern Maryland.

The criticism came not only from his long list of political opponents but also from veterans groups in the conservative 1st District, which encompasses Southern Maryland, the Eastern Shore and Harford County north of Baltimore.

Dyson survived a close reelection challenge in 1988 after questions were raised about the operation of his congressional office and his acceptance of contributions from defense contractors. Considered vulnerable again this year, he faces three challengers in the Sept. 11 Democratic primary. Eight Republicans entered the race after the GOP targeted Dyson for defeat.

"The people of this district are not going to like this," one of his Republican opponents, Luis Luna, said of disclosures about Dyson's Vietnam record.

Dyson said Tuesday that he never tried to hide his opposition to the war. But supporters who have worked in Dyson campaigns over the last 14 years said they were unaware that he was a conscientious objector in 1971, at the time a college student deferment apparently was due to expire. Former Dyson press secretary Katie Tucker said she and other staff members asked Dyson about his draft record in 1988, and he said only that he had a student deferment.

Edward Bozel, commander of Dorchester Post 91 of the American Legion, said he couldn't speak for all veterans, but he called the disclosure "a blow to the head . . . . He's been a good congressman, but I'm definitely not happy."

Said J. Douglas Forrest, state political action coordinator for the Veterans of Foreign Wars: "A lot of our fellows are going to be very much incensed about it, I would think."

Under federal Selective Service guidelines, conscientious objector status was supposed to be limited to those who proved their opposition to all wars. Dyson said Tuesday that he told his local draft board that he was specifically opposing American involvement in Southeast Asia. Dyson included information about his draft status -- apparently his first public acknowledgement that he was a conscientious objector -- in a news release issued a day after The Washington Post requested an interview on the subject.

Margaret Goddard, longtime clerk of the draft board in Dyson's home county of St. Mary's, said that the local board approved "CO" status sparingly, generally reserving it for members of pacifist religions, such as the Society of Friends or the Mennonites.

She said she didn't recall any details about Dyson's appearances before the rural county's board.

From 1965 to 1973, more than 1.7 million U.S. men were drafted, and 171,000 men received conscientious objector designations in the 20 years before 1972. According to the Selective Service, 3 to 8 percent of the draft pool in 1970-71 succeeded in getting conscientious objector status.

Yesterday, most of the candidates opposing Dyson challenged him to reconcile his draft status with his support in Congress for military actions and his acceptance of $102,000 from defense industry political action committees.

In an interview with the Salisbury Daily Times on Aug. 9, after Iraq invaded Kuwait, Dyson was quoted as saying the United States should not rule out the use of nuclear weapons in the Mideast.

"Frankly, I encourage President Bush to pre-position our troops right in the middle of downtown Baghdad," Dyson said.

On May 23, 1989, Dyson inserted into the Congressional Record a Memorial Day tribute to veterans from his district, including those who served in Vietnam.

Dyson has an 80 percent rating with the VFW, and a spokesman in Washington said he would be endorsed this year for reelection and is eligible for a campaign contribution. VFW PAC director Bob Currieo said the organization is not concerned with the military record of a member of Congress.

Dyson said Tuesday that his draft status had no bearing on his strong support for veterans and defense issues in Congress.

In Salisbury, Bill McCallum, a past VFW post commander, said Dyson has worked diligently for veterans. "What he did as a young man has no bearing upon what we know he is as a congressman," he said.

At a news conference yesterday in Cambridge, Dyson noted that all of the soldiers sent to the Mideast are volunteers. "I have not supported a draft and would not support a draft," Dyson said, according to a tape of the interview made by WBOC-TV.

But Dyson has shown by his votes in Congress that he is not opposed to preparing for a draft. On July 28, 1982, Dyson voted in favor of an amendment that prohibited federal education assistance to any young men who did not comply with the law requiring registration with the Selective Service. Staff researcher Bridget Roeber contributed to this report.