The Old Guard, the elite Army ceremonial unit at Fort Myer, is drumming soldiers out of the service -- not for lack of spit-and-polish, but for allegedly being homosexual.

Four soldiers face dismissal in an ongoing investigation that began in mid-October after a member of the unit complained about an incident involving a homosexual serviceman, according to Pvt. Todd Cosper, an Old Guard soldier and acknowledged homosexual.

It is Army policy to discharge homosexuals from the service, an Army spokesman said this week.

"It's just incompatible, period," said the spokesman, Capt. Robert Kramer. Homosexuality, Kramer said, "impairs accomplishment of the military mission."

The Army's policy, and similar policies in the other services, have been upheld in court tests.

Cosper said that he is being discharged because a drug test indicated that he had used marijuana, and he said that four others in the unit are being dismissed for allegedly being homosexuals. Their names were not released.

A spokesman for the Military District of Washington, Lt. Col. John Myers, declined comment yesterday on how many Old Guard soldiers were being considered for expulsion, pending the outcome of the investigation. He said that all the servicemen under investigation are members of the Old Guard's headquarters company in Arlington.

The Old Guard has about 1,100 members, divided into seven companies. Most perform ceremonial duties at such high-profile locations as the White House and Arlington National Cemetery. The headquarters company performs support and administrative functions.

Myers said that the servicemen under investigation are not assigned to sensitive duties that require security clearances.

Cosper, 25, a native of Long Island assigned as an Old Guard journalist, said that he was questioned about homosexual activities about six months ago. He said that the Army "backed off" after he and another soldier got help from a lawyer in Silver Spring.

Early last month, after he was found to have used marijuana, Cosper said, he was reduced in rank, fined and confined to his barracks for 30 days. Now he is being dismissed from the Army as "unsuitable for military service," he said.

Cosper said that, although other Old Guard soldiers were disciplined for alleged drug use as a result of the test, he alone in that group is being expelled.

Cosper said he has encountered other Old Guard soldiers patronizing homosexual clubs in the District and estimated that perhaps a tenth of the unit's personnel are homosexuals, or "about the same proportion as the general population."

Cosper, who said that he expects to be a civilian again by Wednesday, said he has concluded that "gays in the Army are doing themselves a disservice. Gays are treated like a piece of dirt. They don't want us there."

"Although we strive to uphold an American's rights under the Constitution," said Kramer, the Army spokesman, "the courts have upheld the military as a unique society." Homosexuality, he said, has an adverse impact on "discipline, good order and morale" in the ranks.

"We ask, when they sign up," Kramer added. "If they admit it, they don't get in."