One night the prince of Qatar walked into the restaurant with an entourage. Dominique, who knows a hungry prince when he sees one, whipped off his coat, hurried into the kitchen, made fresh vegetable soup, cooked steaks, tossed a salad and made dessert.

"But I treat all my customers the same," says owner Dominique D'Ermo. And he does, almost. Another customer, with neither royal blood nor connections, recalled an evening he stopped in with his wife: "It was something. Dominique introduced himself, talked a while, and when we left, he was standing at the door handing out roses to all the women."

Dominique's, a French restaurant that serves such rarities as hippopotamus meat and wild boar and attracts celebrities ranging from Vice President Mondale to Elizabeth Taylor Warner, is the latest in a long line of "in" Washington eateries, one of the most popular places to see and be seen on the hot Washington restaurant circuit.

Having an "in" place means attracting the "right" clientele. And to lure that clientele takes the right combination of select ingredients: crafty maitre d', distinctive food, convenient location for the "right" people.

"To be an 'in' restaurant is not the most difficult thing," Dominique said yesterday, sipping a cold beer and listening to the, yes, Mexican street-band he had ordered up for his sixth Bastille Day celebration. "The trick, my friend, is to stay 'in.'"

In his lovely Gallic accent that never seems to change -- a friend once quipped, "He goes to Berlitz once a week to keep it" -- Dominique offered some of his own recipes for success: "The menu has to be different, and you cannot have a flat-shoes maitre d' with a hand out.

"I want the most happy restaurant in Washington. People go out to be entertained. Anyone can fix a good steak or a good salmon. We like to make them happy before, during and after the meal."

Sophistication is a strange word to Dominique. "The man who picks up my trash comes with his wife for dinner and he is king for the night."

And it is precisely that lack of pretension (plus prices on the low side among French restaurants) that appealed to Carter administration officials, who began frequenting the place, adding to its popularity. "Patrons don't like to get ripped off. We make them comfortable, like it is in my own living room," said Dominique.

Born in France in 1927, Dominique fought with the French underground at age 15, was captured by the Nazis and deported to Germany and escaped to join the French Army at 16. After the war, he learned to be a superb pastry chef, then took off to serve in some of the world's finest hotels, becoming a cook and hotel executive. But his first love is hunting and fishing -- which may explain some of the off-beat dishes he serves.

"One time, we drove 190 hours in a jeep from Lima, Peru, high in the Andes Mountains to fish for the largest trout in the world.

"Another time I traveled to within 32 miles of the North Pole to shoot a polar bear with one bullet, and won a bet of $1,800."

Now most of his time is taken up with business, and he is a wealthy man. With a sweeping gesture of his right arm toward the tables, he says, "Look, fresh flowers every day. I like to have a rose for the lady.

"Friendly waiters, all different kinds," as he calls one over to introduce him, saying, "He fought with the Spanish Blue Division on the Russian front in World War II and had his leg frozen.

"There," he adds, pointing to another waiter standing by the bar. "His father owned a whorehouse in Marseilles.

"We have 110 different dishes. Look at this menu. All nice fresh foods. Nothing frozen; if you have frozen food you do not have a cook, you have someone to warm them up."

To have a successful restaurant one must have a good lieutenant, and part of the success of Dominique's has been Diana Damewood, a Washingtonian known widely by customers as an extension of Dominique's right arm, and sometimes both arms.

She also learned a lot from from Dominique, to "look at the customer's face, to see if things are right. Are they anxious? Relaxed? Do they need food? Water? Look at their faces.

"As for cooking," she added, "I wouldn't know what to do with a frying pan in my hand."

Dominique, his tie never having been tightened throughout the long day, sits at his bar at 2 a.m. the other day, having said good night to all his help.

His weariness shows with a wan smile. His day had begun at 6 a.m. when he called his greengrocer, butcher, fishman and baker to make selections for his restaurant tables with the care and fussiness of a French housewife buying for her family.

"My friends are picking me up at 4 a.m., a little while from now," he says. He is going fishing. He might even serve up the fish to some customer the next night.

"Someday, I would like a small farm with a swift trout stream where I could raise my own rainbow trout."

But for now he is otherwise occupied. One patron observed: "The crowd mood changes fast in this city. Maybe the scene could shift a year from now. But right now he is basking in the spotlight and the place has personality and he has the energy to hold it."

Leaning out the window of his Cadillac as he departs, Dominique waves and says, "Tomorrow all these people will have to eat, and Dominique will make them happy."