A consulting service named "Chicken Little Associates" goes into business here next week. Its purpose? To alarm clients into thinking about what could happen when Skylab falls from orbit in the next 18 months.

"Nothing this big has ever broken up in the atmosphere before in the 20-some-odd years things have been flying in space," said Alex Fraser, one of two Washington computer experts in the process of forming Chicken Little Associates. "We want to let people know what's going to happen when this big 80-ton beast breaks up and falls back to Earth."

To hear Fraser and his colleague Sam Greenlaw tell it, the National Aeronautics and Space Administration isn't telling it like it is. The space agency has said that most of the pieces of Skylab that survive the heat of friction when they re-enter the atmosphere "may be floating like leaves" by the time they strike Earth, a simile that doesn't impress Fraser and Greenlaw with its precision.

"The way we figure it, the largest Skylab chunks may strike the Earth at 2,000 feet per second," Greenlaw said yesterday. "That's not much slower than the velocity of a rifle bullet when it leaves the barrel."

Three things about Skylab worry Fraser and Greenlaw: its 3,000-pound, lead safe that protected film from cosmic ray damage, its 20,000-pound airlock and its thousands of solar cells that could shower the Earth with glass when they break up in the atmosphere.

"I can't think of anything they could have put up," Greenlaw said,"that could do more damage when it falls to Earth than that lead safe."

The space agency says that the chances of anyone's getting hit by a piece of Skylab are about as remote as getting hit by a meteorite. Again, Fraser and Greenlaw don't like the comparison.

"That comparison was made for people living anywhere on Earth," Fraser said. "But for the people who live right under Skylab when it breaks up the chances are about 16 million times greater, about one in 150 to be precise."

Of course, there's an excellent chance that Skylab will break up over one of the world's oceans and do no damage to anyone or anything. But Fraser and Greenlaw don't like those chances either, which is why they think their computerized service -- estimating Skylab viewing, arrival and breakup times for media and municipalities everywhere -- will sell briskly.

"When this thing starts breaking up, it's going to light up the sky," Greenlaw said. "Every police department in its flight path will get a phone call. They can't afford to be without our service."