William (Dirk) Diefenbach was one of the most well-known figures on the homosexual nightclub scene here in the mid-1970s. A professional disc jockey, he was said to be able to "make or break" disco records locally with the play he gave them at clubs and private parties. In some circles he was known as "the king of disco in Washington."

On Sunday, the 35-year-old Diefenbach, of 2900 Connecticut Ave. NW, died at Capitol Hill Hospital. He was the sixth Washington resident struck down by Acquired Immune Deficiency Syndrome (AIDS), according to the federal Centers for Disease Control.

Diefenbach's death from AIDS, which weakens the body's immune system and thus its ability to fight off disease, is the latest of a growing number in the Washington area.

In the District of Columbia, doctors have reported 19 cases of AIDS, with six deaths, according to Betty Hooper, a spokeswoman for the Centers for Disease Control (CDC) in Atlanta.

In Virginia, 17 AIDS cases have been reported, with two deaths, state officials said. Among those areas where cases have been reported are Richmond, Norfolk, Alexandria, Grayson, Charlottesville, Arlington, Fairfax, Tazewell and Newport News.

In Maryland, 15 cases of AIDS have been reported to the state health department in the past 18 months, with seven deaths, according to health department spokesmen. Nine of the cases were in Baltimore. Maryland health officials have established an emergency regulation requiring all physicians in the state to identify--by telephone or in writing--the names, ages and locations of patients suspected of having AIDS, state health department spokesman John McAvinue said.

Nationally, there have been 1,641 AIDS cases reported, with 644 deaths, the CDC said. Seventy percent of the victims are homosexuals, and most of the rest are Haitian refugees or drug addicts who use needles.

Diefenbach died of pneumonia caused by AIDS, said Michael Bray, D.C. deputy medical examiner. The form of pneumonia that killed him, called pneumocystis carinii, is harmless to most individuals but is harmful to cancer victims who receive chemotherapy, AIDS victims and others whose immune systems are damaged.

When Diefenbach came down with the disease earlier this year, friends shunned him. He was crushed, according to those who stayed with him.

"Nobody came around anymore," said David Brown, who described himself as Diefenbach's lover. "They called, but they didn't come around. Even with gay people, there's a lot of hysteria about AIDS."

Diefenbach, who quit working as a professional disc jockey in 1981 and got a job last year as a clerk-typist at Gallaudet College, apparently came down with AIDS early this year. The first symptom was a severe sore throat that didn't go away, Brown said.

In April, Diefenbach spent several days in Capitol Hill Hospital for tests. Doctors said that he had "compromised immune system" and described his condition as "pre-AIDS." After he returned home, Diefenbach's condition worsened.

"Some days he'd have energy, some days he wouldn't," Brown said. "Many days, he was unable to get out of bed." His temperature rarely dipped below 101 degrees.

"A lot of my friends said, 'Move out, move out,' " said another roommate, R.J. Quinn. "But I knew he needed me. . . . There is so much panic in the homosexual community about AIDS it is unbelievable." Quinn, assistant production manager at Wolf Trap Farm Park, acknowledged that he hasn't eaten in the apartment they shared for months, out of fear of AIDS.

Diefenbach was allowed to return to work June 13, Brown said. He worked that week, but his condition worsened the following weekend. Having trouble breathing, he was admitted to Capitol Hill Hospital's emergency room last Tuesday and placed on oxygen.

"He was such a lovable son, a good boy," said his mother, Dorothy Diefenbach, in an interview from the family home in Columbus, Ohio. "He was never any problem. He was never ill when he was growing up."

Diefenbach died at 5:18 a.m. Sunday, leaving those who stayed with him frightened.

"We feel like ticking time bombs," Quinn said of himself and Brown. "We're being shunned by friends. I may be a dead man."

Quinn added, "Dirk was so talented. We were all drawn by his talent, his charm, his wit.

"It's really hard to face this."