Every year since he moved to Washington, Harold L. Burris has celebrated Gay Pride Day as a symbol of his liberation, free of the constraints that marked his old life as a married Methodist minister in a small Iowa college town.

This year for Burris, and for many of the thousands who will join him today in celebrating Gay and Lesbian Pride Day, the festivities are imbued with a collective sense of purpose.

"Gay Pride Day has always been a celebration of freedom, opportunity and assertiveness," said Burris, 52, "but increasingly it is a celebration of support. There's a real cause now, other than going out and having a good time in the sun."

That cause is AIDS, the disease that many in the gay community say has been both disastrous and inspirational.

Six years ago this month the first five cases of the virulent disease, initially known as Gay Related Immune Deficiency, were reported to the Centers for Disease Control in Atlanta. Since then AIDS has ravaged homosexual communities in many cities, including the Washington area, which ranks fifth in the number of cases reported nationally.

The devastation wrought by acquired immune deficiency syndrome has inspired a powerful sense of community among homosexuals. Private groups like New York's Gay Men's Health Crisis and Washington's Whitman-Walker Clinic, some of which started as shoestring operations in someone's living room, are largely credited with raising public consciousness and prodding the federal government to provide money for research and services.

"Any time there is a sense of real danger, of oppression, it makes people come together," said Victor J. Basile, executive director of the Human Rights Campaign Fund, a political action committee that raises money for supporters of gay rights. "AIDS has made people realize that viruses can find their way into closets, and that all the money in the world and the deepest closet cannot protect someone from AIDS."

Jay Chalmers, a real estate broker and cochair of Pride Day, agrees that AIDS will dominate this year's observance. "Last year AIDS was just starting to come to the forefront of national attention," he said. "This year it is the prime issue on everybody's mind.

"I think there's beginning to be a little sigh of relief that it's no longer a gay issue," he added. "AIDS is now a national and worldwide issue," its place assured by media coverage, the Reagan administration's new testing policy and the recent Third International Conference on AIDS, which drew more than 7,000 scientists to Washington.

The pride and relief many feel is tinged with a profound sense of loss. Burris, who directs housing programs for AIDS patients at the Whitman-Walker Clinic, has known 200 people with AIDS.

Basile, 41, knew 25 people who have died of AIDS. "I know so many people who are positive, I don't know what to say anymore," he said. "I can't say, 'Well, there's just a small chance you'll get sick.' And I don't ask many people if they've been tested.

"I can't tell you the number of Rolodex cards I've pulled out of my file," he said. "Some of them I just leave, because I can't bear to pull them out yet."

That sobering reality, Basile said, is reflected in celebrations like Pride Day as "people realize that a lot of those they celebrated with last year are not around this year, and a lot of people around this year won't be next year."

For many, wondering "Will I be next?" is as terrifying as watching friends get sick and die. Researchers say that in San Francisco and New York City, half of all gay men may be infected with the AIDS virus. Scientists predict that at least half, and maybe all of those infected, will develop AIDS.

As of June 11, 1,161 cases had been reported in the Washington area, 85 percent of them among gay men. Nationally, according to figures compiled June 8 by the CDC, nearly 37,000 Americans have contracted AIDS, and more than 21,000 of them have died. Although the rise in cases among heterosexuals has attracted intense public attention, more than two-thirds of the AIDS patients nationally are gay men.

Pride Day organizers predict that as many as 20,000 people will participate in the 12th annual celebration that will begin at noon with a parade from Meridian Hill Park, also known as Malcolm X Park, at 16th Street and Florida Avenue NW to Francis Junior High School at 24th and N streets NW.

More than 100 groups are expected to set up booths as part of the festival, including, for the first time, the U.S. Public Health Service and the Prince George's County Health Department. Both groups will distribute information about AIDS.

The preoccupation with AIDS has affected lesbians, the group at lowest risk for the disease, which is transmitted through blood and semen.

"I think we're working together more in the past few years because of AIDS," said Mary Farmer, 38, the owner of Lammas, bookstores for women on Capitol Hill and at Dupont Circle. For the past 10 years, Farmer has staffed a Lammas booth at Pride Day.

"AIDS has brought into sharper relief the problems we as lesbians and gay men face every day," she said. "When you see friends being dealt with by police wearing yellow rubber gloves, well, people are touched by that."

Basile was one of 64 people arrested June 1 by D.C. police wearing yellow rubber gloves during a protest of the Reagan administration's AIDS policies. Although Basile does not have AIDS, many of those arrested with him do.

He first celebrated Gay Pride Day in 1981, a decade after he moved to Washington and shortly after he decided to "come out" and end his 10-year marriage.

"The first time I went to Pride Day was a very emotional experience for someone who had grown up feeling illegitimate," he recalled, sitting in a downtown office decorated with an old campaign poster of his friend, Rep. Barney Frank (D-Mass.), who recently publicly acknowledged his homosexuality.

"I think being in Washington made it a little easier to deal with," said Basile, the second of four sons of a working-class Italian Catholic family from western Massachusetts. "The climate was more open here."

With the exception of one brother, who is police chief of a small New England town, Basile's family has been supportive and accepting.

"AIDS has given the world the opportunity to meet the gay community and to get sensitized or desensitized," he said. "I think it will be a bridge to the civil rights struggle that lies ahead."

In the life of Harold Burris, who directs a housing program for 73 people with AIDS, the disease is a constant presence. Burris' training as a minister has accustomed him to dealing with death. "Around here," he said, "I'm usually the one who's trying to calm people down."

Burris said his family learned he was homosexual two years ago, when he began working at the clinic. He was most worried about the impact that the news would have on his grown son and daughter. They have been "absolutely tremendous" and unfailingly accepting.

Burris said he does not personally worry about AIDS. "When you pass the half-century mark," he said in a minister's rich baritone, "you'd better celebrate, not worry."

For Burris, who moved to Washington in 1983 from Cedar Falls, Iowa, Pride Day served an important function during a difficult period of adjustment. "It fit my need for an entree into the community and was a way to see activity outside the bar scene," he said. "I was older, gay, single, not part of the black community."

At Northern Iowa University, a school of 13,000 where Burris spent 15 years as an administrator and director of the Wesley Foundation, a Protestant organization, Burris lived what he called "a dual life." He said he often worked with gay students who felt isolated and ostracized, but he did not acknowledge the special kinship he felt with them.

"Twenty years ago there was no choice," said Burris, who separated from his wife in 1978 and is now divorced. "If you had {homosexual} urges and feelings, you put them aside because they were wrong."

At his first Pride Day celebration in Washington, he staffed the Gay Fathers booth, a group he had learned about from a college roommate who, like Burris, was homosexual, divorced and the father of two.

This year Burris is scheduled to receive an award from committee organizers for his work with minorities. When he accepts it, he said, he will remember the close friends he has lost to AIDS.

A 30-year-old man he helped nurse in his final months taught Burris not only "about the pain of this disease, but also about what faith and strength and love are all about."

"Part of this celebration is that we are going to go on, and we have to put in place things that will help us go on," he said. "AIDS has changed things totally, but not everyone's going to die of AIDS. You have to know how to celebrate, how to live after the pain."