D INNER GUESTS ARE MINGLING, AND it's obvious that everyone wants to know Dr. Kent McKnight a bit better. A fashionably dressed woman brings over a tray of mushroom canape's, and McKnight pronounces them good.

The woman smiles and moves on, to be replaced by a young man in his twenties bearing a steaming casserole. "Sulfur polypores," he says enthusiastically. "Very nice," McKnight replies, "but they may be a bit fibrous at that stage."

And so it goes.

Though soft- spoken and scholarly, McKnight is the life of the party. He is an authority on mushrooms, one of the top five mushroom scientists in the world, and this is a recent tasting party at the Mycological Association of Washington, where wild fungi are consumed with gusto.

Although club members have been collecting and eating mushrooms with impunity for years, others have not been so lucky. At least 16 people were hospitalized with mushroom poisoning in the Washington area in 1986, which McKnight says may be connected with the recent influx of immigrants.

"There is a much wider variety of mushrooms in the United States," says McKnight, "and I'm afraid some of these people confuse poisonous species with ones they've safely eaten at home."

Because of his expertise, area hospitals call on McKnight to identify suspect mushrooms that have been ingested. This may happen as often as three or four times a week during the spring and fall, both prime seasons for mushroom fruiting.

McKnight says police officers frequently show up at his Beltsville home, bearing the remains of a mushroom "snatched from a kid's hot little paws."

In many cases, McKnight can identify the fungus on the spot. But if he can't, it's only a short hop down the road to the U.S. Department of Agriculture laboratory, where he does mycological research.

McKnight himself has experienced the effects of mushroom intoxication. In 1958, when he was a newly minted PhD, McKnight was the first person in the country to cultivate a hallucinogenic species of Psilocybe, the infamous "magic mushroom."

He was working at Brigham Young University in Utah at the time, and the fungus was to be sent to a research chemist eager to isolate the active agent, psilocybin.

McKnight consumed some of the mushrooms to be sure they contained the drug, but he is reluctant to describe the "trip" that members of the Janis Joplin generation would later find so appealing.

"Let's just say I was certain that psilocybin was present," says McKnight, a devout Mormon who eschews both cigarettes and alcohol. Then, with a twinkle in his eyes, he adds, "I'll bet Brigham Young must have turned over in his grave!"