There are still about a dozen of them, if you count the two popcorn'n'porn palaces where the silver screens make the goings-on inside the cars seem innocent by comparison. And contradictory as it may seem, the drive-in movie theaters are both flourishing and dying.

They're robust in the movie lingo of "grosses" and "boffo hits," with some theaters averaging $30,000 to $40,000 on a good week -- triple that of an average area hard- top. But they're passing away slowly and surely, victims of high real-estate costs and unpredictable Washington weather.

In the last decade, the number of drive-in screens decreased 17 percent nationally -- while hard-top theaters increased 39 percent. They haven't built a new one here since the '60s, while the Rockville drive-in bit the dust in the '70s to make room for a townhouse development. The old Palmer Drive-In in Prince George's County still stands -- but is used strictly as a weekend flea market. And while the Queens Chapel Drive-In is going strong, it's just a matter of time before Metro moves in. The terminal is planned for right under where the screen is now.

If all you remember about drive-in theaters is back-seat wrestling, or front-seat diaper-changing for a six-month-old who's now 16, here's what to expect and what not to expect from the drive-in theaters in this area should you decide to pack up the family and go this weekend . . .

First, don't expect "La Traviata" or "The Return of Martin Guerre" at a drive-in. Regulars tend to be a bloodthirsty group, with sensation sometimes spelled sinsation as well. One local distributor says that the ideal night at the drive-in would begin with a shoot-'em-up Clint Eastwood cop film, followed by a punch-'em-up Sly Stallone epic, a kick-'em-up Chuck Norris karate film, topped off by a slash-'em-up horror movie.

That's another thing. Although quality may not prevail, quantity certainly does. Triple features are more the norm than the exception. And all this is padded out with cartoons, lots of previews, and plenty of exhortations to visit the snack bar.

If that's not enough and if you suffer greatly from insomnia, you'll want to look for the dusk-to-dawn marathons that crop up around the holidays like Halloween. Usually six or more features on a central theme are shown, with free coffee and doughnuts served at dawn and passes awarded to survivors. Bob Mondello, the public-relations person for Roth theaters, which has the Ranch and 301 drive-ins, reports that the six-feature Chuck Norris karate festival last spring was a "smash" (no pun intended).

Naturally, sitting through three or more features will require sustenance. That's another area where the drive-in abounds in quantity. First, think of every item offered by your neighborhood hard-top theater. Then add pizza, burgers, foot-long hot dogs, egg rolls, and you've got drive-in fare. However, all this is pretty average fare, even by fast-food standards. So you might want to join the families that bring fried chicken, spread the tablecloth across the hood and eat sitting on the bumper. Engine heat keeps the chicken tub warm.

Steve Turner, head of Universal Pictures distribution for this area, says today's drive- in theater scene is a "picnic with visual effects," which may be a perfect description of the way most families attending drive-ins see it. It's a rowdy crowd that will honk horns at the moments where indoor movie- lovers clap and cheer.

The first outdoor arena built in this area was the ABC Drive-In in 1955, erected on a rural road off Indian Head Highway in then far-out Prince George's County. Surprisingly, after nearly 30 years, it's still No. 1 in box-office dollars, although the 1,050-car capacity is surpassed by Virginia's Mount Vernon Drive-In, which has room for 1,343 vehicles and was the first in the area to be twinned.

"We always aimed for a family crowd," says Fred Wineland, who still owns the ABC and three other "ozoners" (as Variety calls them). "From the very beginning, we opened the evening with a cartoon and we still do it today."

This winter, Wineland plans to make the first dramatic change in the ABC since it opened. He'll add two more screens and become the first drive-in in the area to become a triple.

On the other hand, the Redstone Theater chain, which owns nearly 300 theaters, may soon tear down the Lee Highway Drive-In in Merrifield and replace it with a multi-screen hardtop cinema complex.

If you haven't been to a drive-in for some years or perhaps you have children who've never viewed Woody Woodpecker through a windshield, maybe you should pack a picnic and go this weekend. There's no parking fee, no babysitter to pay, and although you'll pay four bucks a ticket, children under 12 are generally free. And that's for two or three movies plus a playground for the kids when they get bored.

It's not the same as viewing "Diva" at the Fine Arts -- but it is an art all its own.