Thirty-year-old Randy Norton, a co-owner of Fritzbe's restaurant in Fairfax City, looked up in horror from his dinner one night recently.

As part of a birthday celebration, two of his young staffers were about to plaster a friend with a pair of whipped cream pies.

As the pies hovered precariously, Norton said later, customers tensed and women guests, fearing the worst, "quaked in their shoes. But instead, the waitresses turned on each other and "sinashed each other in the face." With that, relieved customers cheered and the restaurant belted out "Happy Birthday."

Such incidents might seem extraordinary in other restaurants, but at Fantastic Fritzbe's Goodtime Emporium that kind of activity is not only tolerated -- it's absolutely encouraged as the key to attracting Northern Virginia's growing dining out trade.

With an estimated 10,000 customers a week, many of them families and young professionals, Norton and his two business partners, Michael Ranney, 31, and Jim Farley, 35, seem to have hit on the key to success.

In the last year, Fairfax residents have been practically inundated with new places to eat -- The Upstairs Maid, Mr. Smith's, Caruso's, T.T. Reynolds, Charlie's and P.J. Skidoo's, to name a few. Two Georgetown restaurants, Clyde's and Chadwick's, have joined the competition, with Chadwick's opening this week in Alexandria and Clyde's later this year at Tyson's Corner.

Commenting on the transformation, one lawyer said he remembered a few years back when dining out in Fairfax County meant a meal at his local bowling alley. Now, he said, he has an alternative to the long drive to the District.

"For the same money, I can eat just as well in Northern Virginia," he said.

Of all the recent Fairfax arrivals, no restaurant seems to have tried harder than Fritzbe's to capitalize on the suburban family clientele.

The restaurant balances a mildly racy menu ("The Marilyn Chambers Special" after the prnographic movie star) to amuse adults with giveaway balloons for children and free popcorn for everybody. The jukebox is purposely kept turned up. Even so the proprietors worry that the restaurant "isn't noisy enough."

"Controlled chaos is important," said Norton, who noted triumphantly that the recent birthday incident was "completely impromptu. People do crazy, silly things on their own. That's why we're such a success."

"It's the only place like it. Everything else is Gino's and McDonalds," said one customer, Ina Alexander, whose family, including two children and her VISA executive husband, have begun dining regularly at Fritzbe's.

Fritzbe's formula hinges on attracting what its owners say is the untapped family market through an artful mix of atmosphere, food and service.

"We have filled the void between Ponderosas and Rustlers on the one hand and on the other hand Jolly Ox's and Marriott Dinnerhouses, a void that in this area no one has tapped," said Ranney, who once worked for Burger Chef.

Ranney and Norton, heir to a rendering plant business and a former teammate of Ranney's on the Fort Hunt High basketball team, originated their concept at the similar but smaller Annandale Fritzbe's.

But Fairfax City, with its lunchtime clientele of white-collar workers and the evening family business, lured them and Jim Farley. an accountant, to set up business next to a furniture store in what used to be a Drug Fair.

A customer has only to step through the door to realize Fritzbe's is different. "Rules for this Zoo" a sign at the anteroom door reads. "Any-one caught entering these premises after 6 p.m. wearing a tie is subject to having 'it' cut off."

The decor is turn-of-the-century Victorian. Old-fashioned street lamps and Victorian gaslights provide a light that is carefully dimmed as the night wears on. The back room's ceiling is a multicolored parachute. Just "to be crazy" according to Norton, two carousel horses are used as dividers between the main floor and a surrounding eating area, while the kitchen is deliberately left open so customers, Norton said, can witness the "crazy chaos" that prevails there.

"The first thing I said to myself when I walked in was, 'this would go big in New Jersey,'" said Bill Zack, 22, a Fairfax City resident returning to live in Bloomfield, N.J.

On the theory that customers appreciate somet ing free, popcorn is dispensed without charge from a large machine in the restaurant's center. On the other hand, customers are respectfully urged not to steal the menus. They are for sale, as are the Fritzbe's T-shirts worn by the young staff.

"Balloons, I like to get them. And popcorn, yes," Aaron Wilson, 5, of Mantua, said approvingly the other night as he waited in line with his parents.

Some Fritzbe critics, like Marty Quinn, manager of the competing Molly Magees at Tysons Corner, say that meals are sometimes served cold, while the restaurant's youthful waitresses are prone to disappear after serving the food.

The other night. two businessmen in pin stripes were seated at the bar at the restaurant's rear, nursing beers and glumly observing the goings-on.

"Look at those waitresses," said one. "They must be at least 18, although they look 14. But they don't see you because we're in suits. When we first came in, they thought we were here to see the management."