It screamed again in Mount Vernon early yesterday morning. Ralph Stickman, the Fairfax County game warden who had been waiting for it in the woods, had just given up and started for his car when he heard that eerie, muted wail-like someone being strangled in the shower.

For the last nine months, nocturnal screaming has come from a patch of woods about one mile from the historic home of George Washington. In freezing rain, driving snow and on hazy summer nights, it has echoed through a neighborhood of $150,000 houses. Children have been frightened. Dogs have barked.

This week the Fairfax County police had had enough. They brought out a Park Police helicopter with searchlights to hover above 100 acres of woods. Six policemen equipped with portable radios were told to stand in the woods and signal to the chopper if they found the screamer. They found nothing.

"I suspect it frustrates the police because they have not been able to catch it," said Dr. William Hark, a physician who specializes in aerospace medicine and lives near the howling in the woods.

The police who took part in the search are not talking. "No comment," said search supervisor Capt. Jack Coleman. Thelma Crisp, a resident who used to talk all the time about the sound, has been told to keep quiet.

"The cops told everybody to be low key. Now, apparently, some big mouth has gone and blabbed it all," Crip said.

Some of the other residents in the area where George Washington's slaves once grew wheat and raised pigs were willing to blab. They described the sound as something like a wild boar, really loud frogs, some guy blowing in a wine bottle, a barred (or hoot) owl, a broken microphone on a CB outfit, a parrot, a mouse with an amplifier, a strangled dog, the ghost of George Washington and the ghost of George Washington's pigs.

Michael Berger, a PhD in wildlife management who works for the National Wildlife Federation, has heard the night sounds and says they do not sound human.

"It's hard to describe, ah, it is a series of screams, not really screams, more like wails. They seemed to be fairly close to Thelma's house," Berger said. His opinions, according to a spokesman, do not necessarily reflect an official view of the National Wildlife Federation.

And Thelma Crisp, who lives on Union Farm Road, isn't talking anymore. She has told several neighbors that she's seen a creature in her backyard that stands 6 feet tall and walks upright. But the police, she reminds the curious, have told her to shut up.

Game warden Ralph Stickman and other county animal agents, suspecting a hoax, have combed for several months the swampy woods that lie between the subdivisions. They have sat in the woods all night on several occasions and listened. They shone their flashlights into almost every tree and bush, looking for loudspeakers. They have came up with nothing.

"The thing seems to know when you leave the woods. Then it will holler. I don't know what it is, to be frank," Stickman said yesterday.

At social gatherings among the predominantly upper middle-class professionals who own houses in the Union Farm Estates and Southwood developments, the thing-called the Mount Vernon Monster in formal conversation-monopolizes party chatter.

"It (the screamer) is all anybody can talk about," said Joan Flore, who lives across the street from the woods.

Frequently feature at such parties are tape recordings of the screamer, made by neighborhood children who hold portable cassette recorders out their bedroom windows in the middle of the night. Party guests often are asked to say what they think the noise sounds like.

Flore, who has heard the tapes too often, said she is getting a little sick of the noise. "Now that it's getting warmer, we would like to be able to open our windows at night," she said.

Responding to angry, sleepless people, the county police on Tuesday assembled two infrared cameras, called in the U.S. Park Police helicopter and stationed men in the woods.

"We hoped that by flying over it, when it started to yell, we could see something," said Maj. Harry S. Sommers, who was reached at police head-quarters in Fairfax City after Mount Vernon area police refused to comment. Sommers said the "thing" didn't yell and the helicopter cut short its search.

"I'm not really sure it is a police problem anyway," said Sommers, somewhat disconsolately. The screamer has not harmed anyone, although several residents have reported that it eats food place in the woods.

Maggie Oyer, who lives beside the woods, said she isn't worried for her safety or that of her two children.

"I don't think it's anything heavy. It would have come out of the woods by now," she said. CAPTION: Illustration, no caption, By William Coulter for The Washington Post