Like ugly little toadstools, the jokes spring up from the gloomy loam of disaster.

Usually they are very sick.

Sometimes they are even funny.

Within a day or two, three at the most, practically everybody has heard them.

And nobody knows where they came from.

About everything from Bhopal to Chernobyl, sparing not even tragic, murdered Leon Klinghoffer, it is as though some evil little demon is whispering them into the ears of at least one person in every city, every office at virtually the same time, simultaneously spreading an irresistible compulsion to infect a neighbor.

The Soviet nuclear sick-joke fallout began before the first dispatches were in print, producing seemingly instant and ubiquitous bad taste. You called your sister, brother, old college roommate in San Diego or Madison or Peoria and sure enough, if he hadn't heard them yet, somebody in his office had.

Question: What are they serving for dinner in Kiev tonight?

Almost nobody ever owns up to creating them, though someone claimed that the key joke on last month's disclosures regarding Kurt Waldheim's past first came out of Time magazine's Chicago bureau. (Q: What's Waldheimer's disease? A: Getting old and forgetting you were a Nazi.)

"Saturday Night Live," in its halcyon days, its apotheosis of tastelessness, often played off disaster: Remember its classic Three Mile Island skit with a radioactive Jimmy Carter as big as King Kong? (Some of the Kiev jokes are actually TMI retreads, but who cares?) And Johnny Carson occasionally gets a few off in his monologue.

But SNL is past its (not ready for) prime; Carson hasn't been around this week and substitute host Joan Rivers is more concerned with breasts than with blasts.

Answer: 180-pound lobster.

The SNL spawn of daytime deejays -- the fifth-graders' prime source -- is currently the chief mode of communication of the inelegant to the downright obscene. But the airwaves have been unusually reticent this week.

Elliott and Woodside of WRQX-FM (Q-107) got some Kiev jokes on the air -- very early, when only the fifth-graders were listening. WAVA's Don Geronimo has been doing little satiric skits mostly around the lack of information, but, a WAVA spokesperson said, "he thought there was a line he shouldn't cross." The Greaseman, at DC-101, under no such constraints, was heard to repeat "a tasteless, sexual and very funny" joke linking Svetlana Alliluyeva with the accident.

And Chris Core at WMAL has been making them up and "circulating them around the station," publicist Pat Ryan said, "but not for use on the air. It's not our style." (Example: What's the recipe for chicken Kiev? Answer: First preheat the city to 2 million degrees.)

Almost none of this proliferating breed of racy radio "personalities" matches the mostly unlamented and long-gone Howard Stern, who phoned Air Florida the morning after the crash and asked the price of a one-way ticket to the 14th Street Bridge. If nothing else, it helped write his ticket out of Washington.

There is one theory that holds that most of the jokes are made up by crazed stockbrokers in New York and then disseminated by quotation. But never mind how they spread -- by radio, TV or just a lot of people reaching out and touching someone -- the jokes may actually serve a purpose.

Samuel Shem, author of the cult medical school classic "House of God" and the more recent "Fine," a novel about the metamorphosis of a psychoanalyst, is a psychoanalyst himself.

Shem -- a nom de plume designed, he says, to protect his patients -- thinks Freud was not completely off base in his joke analysis.

Q: What's tomorrow's forecast in Kiev?

Says Shem, "Freud felt jokes were the only acceptable expression of hostile feelings. I think these events are so horrible that what can you say? So people vent their anger in this kind of way.

"People can't just say that something is horrible and that they feel terrible -- they have to close it off."

As his character Dr. Fine says in the book to his wife, a would-be stand-up comic: ". . . Freud discovered that jokes are an expression of hidden aggression -- repressed, disguised, and expressed in a way that is acceptable. Jokes result in the release of libidinal energy in the phenomenon of laughter." (Freud, who was not noted for his humor, wrote "Jokes and Their Relation to the Unconscious" in 1905.)

A: Cloudy and 400 degrees.

Dr. Frederick Goodwin, director of scientific research at the National Institute of Mental Health, feels that these postdisaster jokes are "legitimate coping mechanisms.

"They offer a sense of relief and give a feeling of mastery over a scary situation."

Goodwin speculates that when something is of such enormity that it changes everyone's lives -- such as the Kennedy assassination -- "the magnitude is beyond what people could defend against. There was no way not to be personally devastated," so there were no jokes.

"On the other hand, disasters at some distance are more available for humor and other coping mechanisms.

"I think," said Goodwin, "that is a healthy, understandable reflex, just as is the classical gallows humor that goes with people who have to do things themselves, which, if looked upon straight on, would be somewhat of a turnoff."

Such as the hangman who named "gallows humor," the precursor of the sick joke. Operating room surgeons and nurses fall into this category, he said. "The humor plays on contrasts and on things not seeming to fit. It does it best by exaggeration."

He also speculated that media overexposure to disaster can provoke a reaction of overtrivialization. "Maybe one is reacting to media portrayal and the joke is a way of saying 'enough already.' "

Basically, said Goodwin, "I think the humor is a reasonably healthy mechanism."