The screen is filled with spinning shapes -- squares, L's and Z's. They drift, then plummet to the ground. Neat rows form as human hands drive this alphabet of falling snow.

This is Tetris -- one of the hottest-selling video and computer games around.

Forget guns and explosions. Tetris is about geometry, not war. Players manipulate the sinking shapes to fill in holes and form complete rows. If a level fills, it disappears, and all the other pieces drop a notch. When holes remain, the pieces stack higher and higher until they fill the screen.

The game is simple, but strangely compelling.

"I would come home and say, 'I'll play one game,' and end up playing 10," said Georgetown University law student Karen Conant. "You start seeing the shapes in your head when you're reading a book or talking to people."

"My girlfriend and I would get into fights over who got to play. We would rip each other off the chair," said Michael Hirschorn, an editor at Esquire magazine.

A top-selling game for personal computers since 1988, Tetris spread its tentacles into a much broader network last year when Nintendo brought it out for its regular home video game and the hand-held Game Boy. More than 2.5 million copies later, Tetris is Nintendo's top-selling title for the first few months of 1990, according to company spokesmen.

What's the fascination?

It's hip, in tune with the times. Tetris is the ultimate glasnost game -- the first Soviet computer challenge to cross the Iron Curtain. Created by Alexey Pajitnov, now a 35-year-old programmer at the Soviet Academy of Sciences, the game reached the United States by way of Eastern Europe and Great Britain.

Take a tour of recent Soviet history with California-based Spectrum HoloByte's edition of Tetris for personal computers. Packed in a bright red box labeled with Cyrillic script, the personal computer version surrounds the playing field with pictures of hockey players, space stations and Moscow's Red Square that change as the game gets harder. Spectrum HoloByte has sold more than 150,000 copies and won a host of "best game" awards.

Catchy Russian folk tunes complete the package on all versions of the game.

"I was sitting in classes, and I was hearing the music in my head. {I would think} 'Stop, stop. Please stop, I'm in the wrong place!' " said Christopher Donesa, 23, who plays on the hand-held version.

Unlike most computer or Nintendo games, which appeal primarily to male teenagers and young adults, according to Nintendo and Spectrum HoloByte spokesmen, Tetris attracts fanatics of both sexes and all ages. "It's a 2-to-92 game," said Nintendo's Bill White.

Not everyone will confess his addiction publicly.

Five-year-old Peter Vaughan of Alexandria freely admitted he has played the game often and that he now can reach the 10th level, where "the pieces come down so fast you're out of control."

But Gil, a reporter for a major metropolitan daily who played Tetris "largely as a time-wasting device," asked that his last name be omitted because "people would laugh."

The game seems to have a particular attraction for law students. At George Mason University's law school, two of the eight coin-operated video games next to the cafeteria are Tetris machines, and a third features Blockout, a variation on the same idea.

Surrounded by a group of fellow first-year law students, Steve Thurber, 26, deftly manipulated the brightly colored falling shapes. "I just got started a week ago, and it's controllable. Only a buck a day," the Vienna resident said.

"You have to be sort of compulsive and want to put things in order," said Donesa, a Duke University law student.

George Mason law students and faculty agreed that video game addiction and good grades come together, although the graders are less sure that Tetris actually improves class performance.

"Virtually everyone who is at the top of their class is also addicted to the games," said GMU night student Katie O'Meara, 26, who has played Tetris for two years and stands in the top 10 percent of her class.

Spectrum HoloByte has already introduced Pajitnov's second game, Welltris, a three-dimensional variation on Tetris's falling shapes, and marketing director Rita Harrington predicts the new game will sell as briskly as its predecessor.

Many recovered Tetris addicts don't even want to look at any more spinning shape games. "It's like getting over a drug addiction. You have to go cold turkey," Hirschorn said.