When a 26-year-old waiter tried to return to his job at Washington's exclusive Cosmos Club last summer after recovering from a rare form of pneumonia associated with AIDS, he learned the position he held for five years had been filled.

Although a specialist in infectious diseases certified that the man was "fit to return to work" and showed "no indication of any disease he could transfer to those he could serve as a waiter," club officials refused to rehire him in any capacity.

"Nobody said to him, 'You can't work because you have AIDS,' " said Irving Panzer, chairman of the club's legal affairs committee. "But if you went into your favorite restaurant and your waiter was known to have AIDS . . . would you stay? Until medical science says to my satisfaction that you can't get AIDS that way, then I'll say there wasn't any job for him."

According to medical authorities, there is no evidence that acquired immune deficiency syndrome is transmitted except through the exchange of blood products or body fluids, such as semen.

"There is no reason to think that being served by a waiter with AIDS would present a problem," said Dr. Henry Masur of the National Institutes of Health, a leading specialist in the treatment of AIDS victims.

The waiter's experience, however, typifies the widespread fear and misinformation that continue to surround AIDS, a deadly incurable virus which has been designated as the nation's number one public health problem. The federal Centers for Disease Control reported last week that so far this year 3,821 cases have been reported, a 74 percent increase over 1983.

For its 7,000 victims, most of whom die within two years of diagnosis, the pain of AIDS is not just physical. Because 75 percent of AIDS patients are gay men, they are confronted with both the stigma of homosexuality and the ostracism that accompanies a frightening and frequently misunderstood disease.

AIDS victims are often fired from their jobs, deserted by their friends, evicted from their apartments and shunned by their friends and families precisely when they are most vulnerable.

"AIDS is the leprosy of the '80s," said Judy Polachek, assistant director of Washington's St. Francis Center, a counseling service for the terminally ill.

Two years ago when AIDS was first publicized and the number of cases was mushrooming, fear over its contagion reached a near-panic level among the public and some health care workers. In some hospitals, medical personnel, afraid they would become infected, refused to touch or treat AIDS victims. Since then some of the fear, at least in the medical community, has subsided, in part because there are no documented cases of anyone contracting AIDS by caring for patients.

In recent weeks new disclosures about AIDS have generated renewed uneasiness in the medical community and revived old misconceptions among the public.

The incidence of AIDS, which public health officials had initially predicted would level off, instead shows signs of increasing. According to preliminary studies, as many as 300,000 people may have been exposed to AIDS, which has an incubation period of about three years, the CDC reported last month.

The disease, initially confined to gay men with numerous sexual partners, users of intravenous drugs, Haitians and hemophiliacs, is now showing up among heterosexual women who had sexual contact with bisexual men. In some cases these men showed no symptoms of AIDS but may have unwittingly carried the disease.

"The hysteria is abating somewhat, but it's being replaced by a more quiet fear," said Polachek. "There is so much misleading information and so much fear people really do think casual contact is enough."

Fueling the fear was an announcement by researchers in October that the virus had been found in the saliva of persons who showed preliminary symptoms of AIDS. Although the meaning of this finding is unclear, doctors say they doubt that saliva is a primary method of tranmission.

"After the saliva thing came out, my husband came screaming into the bedroom waving the newspaper and said, 'You're going to kill me yet' " recalled Polachek, who has at times kissed AIDS patients on the cheek or shared a drink with them. "It worries me a little more than it used to. I'd think twice about sharing a glass of beer with someone."

Even before the saliva finding, AIDS inspired fears of contagion. "All of a sudden nobody wanted to sit next to me or pick up the telephone after I'd used it," said R.G., a 28-year-old Northern Virginia communications clerk on disability leave from C&P Telephone Co. "My father said maybe God was punishing me for being a faggot." One of the most painful memories of his recent visit to his parents' Midwestern home, he said, was drinking coffee out of a Styrofoam cup while his parents used china mugs.

When the family of a 29-year-old Northeast Washington man learned he had AIDS, they refused to let him use the bathroom, although his mother is a practical nurse. He takes his meals on a tray. Once a day, according to a caseworker who has visited him frequently, his family brings him a bowl of water and a wash cloth.

Last April Henry Sparks of Chicago, a 30-year-old AIDS victim, traveled to Washington for emergency medical treatment at NIH on a Piedmont Airlines flight from Dayton under an assumed name and wearing sunglasses to hide his face.

Sparks told two friends that he traveled that way because the day before, when he had become ill and was taken off a Piedmont flight at Dayton, the airline had confiscated his ticket and told him he would not be allowed on any future flight because he had AIDS.

Don McGuire, a Piedmont vice president, said he does not know what happened to Sparks' ticket or why he flew under an assumed name. McGuire said he ordered Dayton officials to transport Sparks to Washington after determining that he presented no danger to other passengers.

But Paul Deeter, a Toledo computer engineer, said Sparks, who died in September, told him he had no money and no way to get to Washington. Deeter flew to Dayton, bought Sparks a ticket as "Tom Spark," and accompanied him to Washington.

These incidents, doctors say, illustrate unnecessary concern about the contagiousness of AIDS.

"The doctors at NIH use the same bathroom facilities and eat in the same cafeteria as the AIDS patients," said Masur. "When physicians stop believing what they say they'll stop eating in the cafeteria and going to the bathroom."

But even at NIH, one of the leading centers of AIDS research and patient care, concern about the contagiousness of AIDS varies. Members of the optical photography department routinely don a hospital gown and mask when photographing AIDS patients, although epidemiology officials have repeatedly urged them to abandon the practice, saying it is medically unnecessary and makes the patients feel even more stigmatized and isolated.

AIDS paranoia has a reverse twist. Because the disease destroys the body's ability to resist infections and cancer, some patients take unusual precautions in an attempt to avoid contracting infections such as a cold, which could prove fatal. One NIH patient was so afraid of the germs at O'Hare International Airport that he flew to a smaller airport when he traveled to Chicago.

"Basically everybody's anxious about the disease," said Deborah A. Newmark, a clinical social worker at NIH who founded a support group for AIDS patients and their families. "Among the general public the hostility is very up-front."

That was what J., a 37-year-old Northern Virginia hairdresser, discovered last month after he was described in a Washington Post story about an AIDS support group of which he is a member.

Shortly after the article appeared, the man, who had not been identified by name or occupation, received a telephone call from his irate boss demanding to know why he had been interviewed.

"He said they had figured it out from some details and that everybody in the shop was up in arms because they thought I was contaminated," recalled J., whose account of the conversation is verified by his employer. "He suggested I come in and clear out my things at night, after everyone had left and then he told me I was fired. He said, 'I don't usually do this, but I'll pay you $500 as two weeks' severance pay.' "

"I was devastated," said J., who had not explicity revealed the nature of his illness to his boss of five years or his coworkers because he feared their reaction. "It was ludicrous. Here I was ashamed of what I was dying from."

J.'s boss, who said he had suspected for several months that his employe had AIDS, said he fired him on the advice of his doctor and attorney. "I felt I had no other choice," the shop owner said. "I hated to have to do this but . . . he's the guilty party if there is such a thing. I don't feel I have the right to make the decision about exposure for my customers. It's his fault, his life style that has caused this."

For victims such as J. and their families there is little or no legal recourse if they are fired or evicted. Some states, including Virginia, where J. worked, essentially permit employers and landlords to fire or house whom they choose.

Even in cases where local laws afford some protection, most AIDS victims are discouraged from filing lawsuits because of publicity and the likelihood they they would die before the case ever comes to trial. Others attempt, as J. did, to negotiate informal agreements that generally involve persuading employers to continue health insurance coverage for several months.

Most AIDS victims and their families learn quickly that honesty is rarely the best policy. Some go to great lengths to conceal the nature of the illness even after the victim's death.

A 37-year-old Montgomery County woman whose husband died of AIDS last summer told her close friends, her parents and even their child that he had cancer. Only her sister knows the truth. "It was awful not having anyone to talk to," the woman recalled. "Day after day I had to come to work and listen to people make jokes about AIDS and just keep my mouth shut."

Her silence was especially painful because she was forced to leave her husband home alone while she worked. "I called every nursing service I could find, but when I told them he had AIDS, they said, 'Forget it,' " she recalled. "So every day I would get my child ready for school, then race to work where I had to smile and be on time."

Often she returned to work to discover her husband had fallen out of bed and was lying on the floor, unable to move. "He was big and hard to move and my child and I would have to drag him up on the bed," she said.

She does not plan to tell anyone why her husband died, especially their child. "It's awful having to keep everything inside. But I don't want to destroy the good memory people had of my husband. He suffered enough."