Open for lunch Monday through Friday, 11:30 a.m. to 3 p.m.; for dinner Monday through Saturday, 6 to 11 p.m., Friday and Saturday until midnight, Sunday, 5 to 10 p.m. AE, D, MC, V. Reservations. Valet parking for dinner. Prices: Main courses at lunch $4.25 to $7.95. Main courses at dinner $10.50 to $18; full dinner with wine, tax and tip $25 to $40.

You can teach old Guards new tricks. Long a Georgetown site with attractive possibilities, the Guards has been polished and revised to fit that most promising of new restaurant trends, a grill. Several restaurateurs have talked lately about opening a grill restaurant, specializing in charcoaling meats and fish, but while they talked, T. Gregory's has done it. And done it exceedingly well.

No opportunity to make a good impression is ignored. The telephone greeting is gracious, volunteering that there is valet parking in the evening. The valet reminds you to present your parking token to your waiter 15 minutes before you plan to leave so that your car will be waiting.

Inside, the thoughtfulness continues apace. From waiters to busboys, the service is dignified. Waiters are familiar with the food, know which fresh herbs are used with which sauce, and keep a watchful eye on your table from a distance. The service was so considerate that on my first two visits I thought I had been spotted as a restaurant critic, though I had not.

Beyond the monumental curved bar are two small seating areas with green leather banquettes, tables set with white cloths and long-stemmed yellow roses, tasteful tableware and ornately folded napkins. The view is of solid, dark wood paneling with angular English carving, of an imposing stone fireplace, of mirrors and leaded glass to lighten the mix. Tiny lamps reflect in the polished bare wood floor. It is simple and English, as handsome as Basil Rathbone and of similar vintage. Two large tables set in niches opposite the bar tempt one to invite a group of friends, could one afford to bankroll such luxurious semiprivate dining.

It is a restaurant of character, with equivalent service. And the food isn't even French.

The food is, furthermore, very good and, in the instance of a few dishes, unexcelled. The menu is small, with 10 standing main courses, all charcoal-grilled, and a couple of non-grilled daily specials. It is quite expensive, with veal, lamb and beef averaging $15 or $16, fish about $11. No appetizer at dinner is less than $4.25 (except soup), and dinner is bound to cost more than $30 a couple if you have done justice to the menu and wine list. Lunch is omelets, quiches, paillards and brochettes, costing considerably less, though up to $8 for platters.

Simplicity does not foreclose imagination, and T. Gregory's has some original -- and successful -- culinary inventions. Getting right to the heart of the matter, an entree called "Graavlox lightly grilled" is an extraordinary idea. Thick salmon steaks are marinated for several days in salt and sugar to cure them (dill is probably part of the recipe, but was not noticeable at the end). Then they are charcoal-grilled very briefly, just so the surface is seared and the smoke has permeated the flesh. But under that slight crustiness, the fish if raw, as one usually eats graavlox. It is wonderful. With it is a cup of homemade mayonnaise flavored with the marinade, unneccessary and not as suitable as graavlox's traditional sweet and sharp mustard-dill sauce.

Each grilled dish at T. Gregory's has its own sauce, whether herbed butter or seasoned homemade mayonnaise or winey meat juices, and some of them are very good, notably the rouille-like pink garlic sauce for the swordfish. But sometimes they are superfluous, and T. Gregory's is clever to serve them on the side in little cups so you have the choice of using or avoiding them.

The menu makes it clear that, though a grill restaurant, T. Gregory's is not a steakhouse. Two steaks are on the list, a bone-in rib steak for one or a New York strip for two. They are good meat, cooked precisely with a seared surface. But they have stiff competition in the thick calf's liver steak, in my experience, and probably in the individual rack of lamb, the Kentucky ham steak and the brace of squab. The daily specials, if my sauteed lamb with tarragon, mint and mushrooms was representative, can be among the best dishes. Even on such a small menu, though, there are missteps. The veal t-bone, a specialty of the house, was good meat but chewy and dry after its charring; the swordfish steak was fresh and beautifully cooked, but it has been a long time since I have found swordfish locally that has much flavor.

Main courses are not even the main excitement at T. Gregory's. Appetizers can be superb, particularly the snails sauteed with mushrooms, bacon and tomatoes and enveloped in a haze of Pernod. If you favor raw meat, try the carpaccio, paper-thin pink slices of beef drizzled with a very tangy mayonnaise. The smoked salmon is of fine quality, and a very interesting alternative is Italian sausage with roasted peppers, moistened with a creamy garlic sauce known as bagna cauda. The sausage did not taste Italian; it was more like English bangers, but the whole mix was succulent. And daily specials are equally satisfying, whether a soup such as seafood with corn or an hors d'oeuvre plate of seafood salad, meat or chicken in homemade mayonnaise and a marinated vegetable. My only complaint of the hors d'oeuvre plate (and of the lunch menu) was the vitello tonnato, which needs more anchovy and lemon zing to its bland tuna sauce.

You will be justifiably urged to order a la carte vegetables, not just because the main courses are unaccompanied, but also because the vegetables are excellent. The fried shoestring potatoes are unbeatable, crisply fried thin strips of Idaho potato cooked in good oil; and the carrot and zucchini emince is shreds of vegetable infused with butter.The brochette of grilled vegetables is slightly less successful, a good idea but ultimately just big chunks of smoky vegetables. For some reason, the menu lists $4.50 portions of vegetables which are actually more than enough for four people. You can order half-portions and certainly should, even for two to four people. Don't expect the menu to remind you of that, but the waiter might.

With the meal comes a cunning little round loaf of well-made sourdough bread.

And then there is wine. The maitre d'hotel has been a wine writer, and it shows. The list is small but ranges from elegant vintages of big name wines to imported house wines in bottles for under $10. Even in the $10 to $15 range are some very good wines, although you must look to the red Bordeaux and the white Loires or Alsatians for such down-to-earth prices. The '77 Beyer Gewurztraminer is seldom seen in Washington, but worth seeking. For after dinner the bar stocks some special armagnac and cognac. And one glorious way of ending a meal at T. Gregory's is with a glass of vintage port, cheese and fruit.

Again, the menu listing of cheese and fruit with port is enough for two (but includes only one glass of port); the price varies with the fruit selection, usually $7 to $10 at dinner ($2.75 at lunch without the port). The fruits may be mangoes and kiwis with more familiar apples, pears and strawberries, all attractively sliced and arranged. The cheeses are likely to be two, often a ripe Boursault that reminds you how sensational that cheese can be.

More typical endings are the house-made pastries; an alcohol-drenched chocolate sabayon torte, a crunchy maple walnut pie and a white cake with strawberry cream cheese frosting that tastes like a typical hometown bake sale cake. All of them, but particularly the walnut pie, are oversweetened; none is as rewarding as the other courses.

Washington has many elegant restaurants, but few of those as good as they are luxurious are neither French nor Italian. T. Gregory's adds a rare American restaurant to their midst.