Atmosphere: Cool.

Hours: 7:30 a.m. to midnight, Monday through Friday; 5 p.m. to midnight, Saturday; closed Sunday.

Price range: $2.75 to $3.50 for salads, sandwiches and quiches.

Credit cards: American Express, MasterCard and VISA.

Reservations: No.

Special facilities: Not accessible to the physically handicapped; no parking; no booster seats or high chairs.

When the owner of a classy, expensive French restaurant upstairs turns the basement into a cute underground cafeteria featuring cuisine economique, it sounds like a great idea. It's even greater in execution, as I found one lunch hour when I went down the stairs into La Detente for a quick bite, found a superb homemade vegetable bean soup and promised myself to return with the family one evening. My kids love cafeteria service -- they like to pick and choose their food.

One evening when we were downtown and programmed for a light meal, we wandered into the underground passage that is La Dentente. Much to out surprise and disappointment, the cafeteria line was closed. It is open only at lunch time, we learned. Dinner hour features a menu and waiter service, but the prices still are economical: quiches, salads and sandwiches are $2.75 to $3.50. Unfortunately, the wonderful hot soups available at lunch were nowhere in sight.

La Dentente is fixed up in a super-severe, art deco mode. The underground warren of rooms is painted white and little is done to soften the angles of the walls and partitions that separate one dining room from another. Decorations consist of blue table cloths, a flower on each table and a series of highly stylized watercolor floral prints. La Detente doesn't have the bright, cheery glow that puts children at ease. One nice touch for the kiddies, though: the floor is linoleum, so milk and Coke spills do no harm. Background music is the mellow singing of a French chanteur.

We started our dinner with two house salads, $1 each. They were first rate: romaine and other lettuces that were extremely crisp, shredded carrots, tomatoes that had some taste and a nice house dressing. Our only objection: the dressing came in a little plastic thimble. There wasn't quite enough for the greens, and what there was would have been better tossed into the salad before serving.

For his main course, my son the vegetarian had the assorted salad, $2.75. The dinner-sized plate was heaped with crisp lettuce, shredded carrots, cole slaw, fresh poached green beans that still had some snap and their sharp green color, olives, avocado and other goodies. His request for bread was answered by the waiter's announcement that the bread was being warmed. We expected a small loaf, a roll or, perhaps, a croissant. Instead there appeared two slices of whole wheat bread, gently warmed without being toasted.

My husband and I ordered quiche, $3.50 for either lorraine, spinach or mushroom. His was lorraine; mine spinach. Both were served on the wrong -- i.e., cool -- side of room temperature, and that took away from the flavor and the blending of cheese with meat or vegetable.Besides, a cold winter's night calls for hot or at least warm quiche. As for the quality of the quiche, the pastry was decent and the bacon and cheese were fine. The spinach spiked with chives didn't work.

My daughter eyed the sandwiches: $2.95 for ham and cheese, chicken, pastrami or corned beef on bread; $3.25 for ham and cheese, corned beef or roast on a croissant. She went with roast beef on a croissant and was rewarded. Juicy, fresh, not-too-thinly sliced, medium-rare roast beef was heaped on a flaky, buttered and warm croissant. The flavors melted together in perfect harmony.

Portions at La Detente were modest enough to leave room for dessert. The menu offered cheese cake, carrot cake or fruit salad, at $1.25 each; chocolate mousse, 95 cents; melon, $1.75, and homemade tart, $1.50. The tarts the night of our visit were peach, pineapple or orange. We tried peach tart and cheesecake. The tart's pastry was crisp and flaky, with a cream filling topped by peaches that were reminiscent of the canned variety. The cheesecake was surprisingly delicate. Not a crumb of dessert was left on anyone's plate.

The tab for our dinner, including two white wines, a soft drink, main courses and desserts for four, and two side salads, was $26.19, including tax. If only the quiche and room temperatures in La Detente had been warmed. We needed our coats tucked around us throughout most of the dinner. Otherwise, La Detente deserves raves. As it was, we thought it was a pleasant, light dinner a la Francais.