The D.C. Police Department is trying to decide how to deal with a policeman who is considering sex-change surgery.

The policeman has been undergoing preparatory hormone treatments at Johns' Hopkins University Medical Center for about a year and a half. During the last two months, his police powers have been revoked and he has been reassigned to nonuniformed clerical work at the same salary while he and the department weigh their next steps.

Police officials were unavailble, or unwilling to comment directly on the case yesterday, but one official did say he could not see how the department could legally dismiss an officer because of a planned or actual sex-change operation.

The officer himself - a widower anxious to remain anonymous in order to protect his three children, he said - was full of praise for the department's "bigheartedness" in handling his case.

"When I needed to reach out, when I was really up against it, they were there," he said. On an undercover assignment when he first sought psychiatric help and then began the hormone treatments, the officer reported the situation to his superiors in accordance with department rules covering outside medical consultation, he said. "My performance was average or better, in all modesty . . . so they didn't wnt to let me go."

After the undercover operation had wound up, "it was my request that I be given a noncontact position, preferably plainclothes," he said. Although he had not asked a be relieved of his gun and police powers, he said he could not criticize the department for taking those steps. "They don't know what they're dealing with either," he said.

The officer said he would not want to leave the police department if he has the sex-change operation. "This is a whole new life, a whole new ballgame," he said. "I may be more at peace with myself, but it's a whole new world so I would rather stay on the same turf."

But if the department decides to retire him for medical or psychiatric reasons, he said. "I am not going to fight it . . .because the last thing I would want to do is bring something that is potentially derogatory on the department . . . and I am not going to put my kids through it."

As a seven-year veteran, the officer would not receive a pension unless his disability were determined to have been caused or aggravated by police duty.

A sex-change operation at Johns Hopkins involves at least two years of psychiatric therapy, hormone treatments, and "living in the desired sex role," which in this case would include wearing women's clothes, according to Amy Burns, coordinator of the Sexual Behaviors Consultation Unit.

A "Gender Identification Commit tee" must then decide if the patient is ready for implant surgery, and if the committee should rule against it, said Burns, the effects of the hormone treatments - typically loss of facial hair, plus some additional breast tissue and roundness of the hips - are completely reversible.

"I made it my business to research it thoroughly before I even began," said the officer, who shows no obvious physical effects from the hormone treatments, although his thinning hair is on the long side and he appears to have trimmed his eyebrows.

He expressed confidence that if he decides to go through with it, he will make the transition smoothly. Fellow officers, he said, "have come up and talked to me about it and they haven't said anything derogatory about it." He added, however, that he had never socialized much with polie officers after hours - "I never went out for a beer with them before, so I won't do it now."

He conceded that he was aware of some jokes at his expense. "They might say, 'Which restroom are you going to use next week,' and I can laugh along with them," he said. "But it'll die off . . . if a big mountain is made of a mole-hill then it will probably become a mountain. Otherwise, I don't provide an excuse by making a fool of myself."

The officer has spent most of his police career on uniformed patrol, he said, with occasional investigative assignments. "I am very strong in English and creative writing and so forth . . . Hopefully, some day I plan on being an attorney," he said. He still has a year to go for his bachelor's degree at American University, he added, but has temporarily dropped classes as a result of his sex-identity problem.

Although police officials and two local civil liberties experts were unable yesterday to cite any court rulings specifically covering discrimination by a police force according to sex preference or sex identity, Franklin Kameny, and official of the Mattachine Society and Gay Activists Alliance and a member of the city's Human Rights Commission, said that he believed the D.C. human rights law would bar such discrimination.

That law prohibits employers from discharging, punishing or segregating employees "based on . . . race, color, religion, national origin, sex, age, marital status, personal appearance, sexual orientation, family responsibilities, physical ha ndicaps, matriculation, or political affiliation.