Thousands of veterans kicked out of the military as homosexuals can now apply for honorable discharges because of a largely unpublicized change in Defense Department policy.

The rules still demand that homosexuals leave the military, but a Pentagon spokesman acknowledged yesterday that a temporary policy allows veterans with a less-than-honorable discharge - including homosexuals - to apply for an upgraded discharge based on their service records.

"The trend has been obvious since March," David Addlestone, an attorney who specializes in military law, said yesterday.

"Veterans can apply for a review of their discharge and if the only reason for the less-than-honorable discharge was that they were homosexual, then they can usually get it upgraded."

Eligibility for veterans' benefits generally accompanies an upgraded discharge.

In March, according to United Press International, the Defence Department issued guidelines saying that a dischargefor homosexuality should be based on a person's record in service and "circumstances" around the homosexuality, but each branch of service makes its own specific rules.

Prior to that, on Jan. 20, UPI said, Navy Secretary Graham Claytor issued a memorandum stating explicitly the Navy policy for homosexuals:

"An individual administratively separated because of his homosexuality should normally be given an honorable discharge unless the quality of his service, as reflected by official service record, warrants otherwise."

Assault and child molesting are considered "aggravating circumstance," spokesmen said.

Franklin Kameny of the Gay Task Force, a homosexual rights organization, who is an expert on homosexuals and the government, said the Navy "has gone from the worst to the best service" since Claytor's memo.

Addlestone said the Army and the Air Force have not yet issued specific regulations but in most cases homosexuals can get their discharges upgraded in those branches as well.

He estimated that 20,000 to 30,000 veterans have received less-than-honorable discharges because of homosexuality.

"Just last week I represented one veteran who was discharged in 1945 because of alleged homosexuality, and he got upgraded," Addlestone said.

Because of the new policy,the 15-year statute of limitations for applying for discharge review has been lifted until Jan. l, 1980.

Addlestone said the military's attitude toward discharging homosexuals "has changed dramatically" since T. Sgt. Leonard Matlovich, a decorated Vietnam war veteran, proclaimed his homosexuality and was expelled from the Air Force on Oct. 22, 1975, after a widely publicized hearing.

In the past, it was not unusual for homosexuals with otherwise goodrecords to receive less-than-honorable discharges. Addlestone, who defended Matlovich, said even a general discharge "under honorable conditions" can hinder a veteran's chances for a job.

Navy statistics show the difference the change inpolicy has made. In the 12 months through mid-1975, 147 homosexuals received honorable discharges while 347 got general discharges. Between Oct. 1, 1977, and June 30, 1978, there were 372 honorable discharges for homosexuality and 276 general discharges.

The Navy never published its new policy.Addlestone and other lawyers with the National Military Discharge Review Project obtained it under the Freedom of Information Act.

"The problem now is that a lot of veterans justdon't know they can apply for the discharge review," Addlestone said.

Two forces helped bring about the change in treatment of homosexual discharges, he noted.

First, the Defence Department was ordered by Congress last October to issue specific guidelines for its discharges and reviews. Second, a number of lawsuits had been filed against the military concerning homosexaul discharges.

"The two circumstances together lead to major changes," Addlestone said.

While supporting the upgraded discharges, Matlovich, Kameny and other gay rights activists are also pressing to end the exclusion of homosexuals from military service.

"Homosexuality or heterosexuality are irrelevant when talking about someone's capabilities" in military or civilian life, Kameny said.

Matlovich, who is now on a speakers' circuit and counsels homosexualsin the armed forces, said homosexuals no longer are just serving quietly in the military. "More gays are fighting back," he said, "and are not leaving [the service] like we used to."