Colorful floats, a marching band, baton twirlers and roller-skating clowns marched down Columbia Road yesterday for the District's 11th annual Gay Pride Day parade. But the celebration had a somber undertone, with the fear of AIDS dominating displays and conversation.

"The festival is more subdued this year than last year," said Richard Witt, a physician's assistant who helped pass out leaflets on acquired immune deficiency syndrome, a fatal disease that frequently strikes gay men.

"I definitely think AIDS is on people's mind more," he said.

U.S. Park Police estimated that more than 1,000 persons gathered at the Francis Park Recreation Center in Northwest Washington after the parade for a festival featuring music, exotic foods and games.

Celebration organizers said at least 7,000 persons participated in the parade and the festival.

Several organizations set up booths to give out information on AIDS or to collect money for AIDS research. A hot air balloon on the festival grounds carried the message "Play it safe."

Marchers carried signs that said "Stop AIDS, money for health care not warfare," and one church group sold buttons that said "God is greater than AIDS."

Bill Chesldine, a 36-year-old accounting clerk at the National Institutes of Health, said four of his close friends have died of AIDS in the past year and two more recently were diagnosed as having the disease. Chesldine said he also comes in contact with AIDS patients at NIH.

"I am scared to death," he said. "I've seen people die of AIDS and it's not pretty."

Ray Zadrosny, 28, sat at a table on the festival grounds soliciting donations for AIDS research for a group called the AIDS Action Council.

"I have AIDS," he said matter-of-factly, as his boyfriend Fred touched his arm gently. "It was diagnosed in March."

Zadrosny, a counselor for learning-disabled adults, said his only hope lies in being accepted into a research program at NIH that is experimenting with a new drug that researchers hope will arrest the disease.

"I'm cautiously hopeful," he said. "The drugs aren't progressing as I'd like them to but at least they are something."

Fred, who did not want his last name used, said he knows of three other friends who have AIDS. "I value my time more now," he said. "I'm not going to let fear overtake me."

Brad Rymph, 30, a member of a group called Mid-Atlantic Affirmation, part of the United Methodist Lesbian and Gay Organization, said concern about AIDS has heightened "the feeling that we have to keep close together."

Rymph said several friends had commented that day about researchers' predictions that about 150,000 persons will die of AIDS by 1991.

But AIDS was not on everyone's mind.

Madoc, 24, and Aaron, 25, strolled arm in arm and munched on slices of kugel, a Jewish dish made of noodles and sour cream.

"We are both here so we can prove we are gay," said Madoc. "It's like a reaffirmation in public that we don't have anything to hide," he said, leaning over to kiss Aaron.

Some, like David Musaria, 33, and Debbie Lee Ridge, 31, a couple from Hoboken, N.J., said they just came to watch.

"My reaction is just to smile," Musaria said. "I don't think anyone here is taking things too seriously so I don't think I should either."

Sydney Griffin, 20, who lives in Maryland, said she came to the festival to sell T-shirts with the words "Vive la difference" printed on the front. She said she had sold 30 in about an hour.