By day, John Coale and his wife, Greta Van Susteren, are high-powered Washington lawyers, waging legal battles during 12-hour workdays.

But at night, they wage battles of a different sort. They plunk themselves in front of the TV and enter the world of Nintendo, where they take on enemy soldiers, evil empires and alien spaceships. Sometimes they even take on each other, fighting over who gets to play first.

"There's this one game called 'Galaga,' a space-invaders game," the 42-year-old Coale said enthusiastically. "I bust 300,000 on it. My son and his friends can't believe it. When they see an old man get that score, it boggles their little minds."

"We're out of the closet," added Van Susteren, 36. "It's a little embarrassing to admit you enjoy something a lot of 12-year-olds do."

They aren't alone. In the few years since Nintendo's debut, the games have grown from a kiddie favorite -- the successor to marbles and pinball -- to a family fixation. Adults have proved to be just as susceptible to Nintendo fever as their children are.

Consider the Besmen household of Silver Spring, one of the thousands in the Washington area equipped with Nintendo machines. All four of the family's members -- Bruce Besmen, his wife, Debbie, and their sons Erich, 11, and Chris, 8 -- play the game, often competing with each other.

"It definitely brings my older son and I together," said Debbie Besmen, explaining that her younger son likes different games than she does. "We definitely spend time together playing that we wouldn't otherwise."

For the uninitiated, Nintendo games are played on what looks like a small VCR attached to a television. Players use hand-held controls to move characters -- soldiers, spies, medieval warriors and others -- across the screen and through their paces.

Although the 200 or so games sold by Nintendo of America vary in complexity, part of their appeal is that most anyone who can press buttons can enjoy the games. The company has even developed a mouth-tube operated "hands free" version for people with limited mobility or who can't hold controls.

Fans attribute the games' enormous popularity to several factors: They're challenging, they sport sophisticated, colorful graphics, and they're downright addictive.

"Even if you score 300,000, you want to score 300,005," said Van Susteren. "You always want more."

The craze is paying off handsomely for Nintendo, which introduced the games in the United States seven years ago and hopes for sales of more than $4 billion this year. It's also enriching video stores, many of which rent the games; an official of Erol's said Nintendo accounts for 5 to 7 percent of the company's rentals in the Washington region.

Nintendo officials take all the fun very seriously. Asked what characteristics Nintendo game designers strive for to hook players and keep them hooked, Dan Coyner, the company's advertising manager, said, "It's just not something we discuss."

Coyner did say that game designers try to come up with games that keep players trying to better their performances. It was a lack of such challenges, he said, that has led to the flameout of other video games.

Nintendo's popularity has had some far-reaching effects, even going so far as to turn parental punishment inside-out. Most everyone older than Bart Simpson can remember being forbidden to go outside to play after misbehaving; nowadays, some area parents say they forbid their children from playing Nintendo for a week, virtually forcing them to find their fun outdoors.

As with any craze, Nintendo has its downside.

For instance, Richard Brasington, a rheumatologist at Wisconsin's Marshfield Clinic, said he is seeing more and more patients suffering from a painful inflammation of the tendon on the back of their thumbs. The swelling, he has reported, is caused by repeatedly pushing buttons on video game controls -- hence his name for the malady, "Nintendinitus."

And as the amount of time spent playing the games has grown, so have some parents' worries. Will Nintendo, they wonder, turn their children into a generation of joystick-wielding, homework-shirking zombies?

To prevent just that, many families have laid down the law.

Yvonne and Cleo Davis, of Clinton, have three children -- Donnita, 14, LaKisha, 13, and Cleo, 10. All of them play Nintendo, but Cleo plays the most, sometimes for four hours at a time.

So the Davises have devised a simple rule: Cleo must spend as much time studying as he does playing Nintendo. Though Yvonne Davis said the youngster probably cheated a little on the Nintendo side, he still earned straight A's during the last school year.