A Washington lawyer who has gained prominence for representing dozens of people involved in AIDS discrimination cases filed a lawsuit on his own behalf yesterday, accusing a major insurance company of refusing him disability coverage because it believes he is gay.

In bringing what is thought to be the first lawsuit under the city's tough AIDS insurance law, Mauro A. Montoya Jr., legal services director of the Whitman-Walker Clinic AIDS Program, said that Connecticut Mutual Insurance Co. denied him coverage last year with no "medically valid justification."

Montoya said in court papers that he is gay. He alleged that Connecticut Mutual, which under District law is not allowed to consider sexual orientation or to question applicants about their sexual preference, was aware of his legal work for AIDS patients and concluded that he was gay and therefore at greater risk of contracting the fatal virus.

Connecticut Mutual knew of Montoya's position with a clinic serving the gay and lesbian community, and his legal work for people with AIDS, according to the lawsuit, which said the company cited a minor medical condition as a pretext for denying coverage to Montoya.

The lawsuit, filed in U.S. District Court in Washington, alleges that Connecticut Mutual's conduct was "outrageous and intolerable in that it offends against a generally accepted standard of decency and morality."

Mike Salius, spokesman for the Hartford-based company, said the firm had no comment on the lawsuit, but said the company does not consider sexual orientation as a factor in whether to provide insurance.

Montoya's lawsuit highlights what he and other legal experts in the gay community say is a real and growing problem for homosexuals seeking insurance: the practice of "redlining" -- the use of various criteria, such as zip code or occupation -- for screening out people who the company thinks may be gay.

Industry executives have worried publicly that the cost of paying AIDS claims could bankrupt their companies, though legal experts say their fears are exaggerated.

While the insurance industry trade groups are on record opposing redlining, the legal experts point to various evidence that the practice is on the rise. A congressional survey of 62 insurance companies released last month shows that 29 percent said they consider sexual orientation in underwriting.

Montoya's lawsuit alleges that Connecticut Mutual's actions violated the D.C. Human Rights Act, which prohibits companies writing policies in the District to discriminate on the basis of sexual orientation, and the D.C. AIDS insurance law, which prohibits redlining and testing for the AIDS virus. However, most other states and municipalities don't have such protections for gay people, according to experts on AIDS litigation.

In his capacity as legal adviser to people claiming AIDS discrimination, Montoya said he has advised about 50 people who believe they had been redlined in some way. However, he and other legal experts said, this is believed to be the first lawsuit in the country in which an insurance company has been accused of denying coverage because of suspicion of sexual orientation.

Montoya, 29, has worked at the Whitman-Walker Clinic for two years, during which time he has done a variety of legal work for hundreds of people with AIDS. He said he plans to resign shortly, citing burnout associated with his work.

His dispute with Connecticut Mutual began more than a year ago, when he said the company solicited him to buy its disability coverage. Montoya said he completed an application in 1986, but early in 1987 the company informed him that it would not sell him the coverage.

In a subsequent letter to his physician, the company said the reason for denying coverage was its concern that he may have sexually transmitted diseases, based on Montoya's medical records indicating that he once suffered from a skin disease called molluscum contagiosum. Montoya and his doctors have contended the illness, which has long since passed, is evidence of no such thing.

Abby Rubenfeld, legal director for the Lambda Legal Defense and Education Fund in New York, said her group has received increasing complaints from people who say they have been redlined. "They apply for insurance and they get it denied, but they were in good health," she said. "You can't assume it is for any other reason than the {companies} believe they're gay."