Open daily, 11:30 a.m. to 2:30 a.m. AE, DC, MC, V. Reservations suggested on weekends. Prices: Same menus at lunch and dinner; main dishes $6 to $13. Full meal with wine, tax and tip aobut $15 to $20 a person.

Instead of a welcome mat, Las Pampas has furnished its entrance with a clud of garlic fumes. And more vivid than a neon sign is its front window onto the kitchen, the chefs forking hunks of beef onto the grill, slathering them with marinade and plunking them onto sizling metal platters before your very hungry eyes.

Thus, from the street Las Pampas seems rough-hewn, informal and somewhat makeshift. Inside, however, the waiters are wearing black tie, and the dining room is paneled with narrow wood slats on walls and ceiling, which is pitched in the form of a tent. The walls are lined with eye-level mirrors, the ceiling hung with crystal chandeliers, the tables set with brown tablecloths on white. A hostess in slithery red dress adds a touch of tropical color. When the piped-in music is Latin -- which is most of the time -- Las Pampas whisks you off to Argentina, with its sights, its sounds and its smells.

But if you are ushered upstairs to the semidecorated and distinctly less pleasant dining room, it's like a budget tour. Resist. The downstairs dining room is half the fun.

Getting right to the meat of the story, Las Pampas is an Argentinian grill, which should mean that monstrous portions of beef are marinated in olive oil, vinegar, oregano, onion, parsley, red and black pepper, garlic and more garlic, then seared on a hot grill. It only partly meets the definition, but the marinade imparts the right taste and smell, and the attempt sufficiently satisfies local Argentinians that they have made it a gathering place.

True to form, allis beef except one chicken dish, probably the best dish on the menu. Also one of the cheapest, at $6.95, it is crisp-skinned with moist flesh and the flavor of garlic and oregano flowing with the juices. As for the beef dishes, it remains a mystery how nine grilled beef entrees on one menu could vary so widely in their satisfaction. Neither price nor menu description are a fair guide, so here is a rundown:

No. 1 -- Baby beef filet mignon, 12 oz., $12,75. One of the top prices and definitely the top beef dish, inches thick and therefore easy to cook rare. (The "mayonnaise" the menu offers with it apparently is a mis-translation, meaning marinade.) Order it.

No. 2 -- New York strip steak, 12 oz., $9.95. Indeed large, though much thinner than the filet, it is cooked rare if requested, but comes out gray rather than crusty. The problem seems to be that Las Pampas' grill is not not enough for searing. This steak has been fatty and greasy, but with careful trimming a decent value. Order with caution.

No. 3 -- Porterhouse, T-bone stead, 14 oz., $10.75. Hardly thicker than a sandwich steak, this was the flimsiest 14-ounce steak I have seen, and overcooked to drynes. Pass it by.

No. 4 -- Famosa parrillada for two, $17.95. "Famosa" refers to the reknown of Argentinian mixed grills in general rather than Las Pampas' version, which consists of dry, chewy sweetbreads and kidneys, blood sausage strong and crumbly and another sausage standard to any pizza shop. Then there were short ribs so tough that the "typical gaucho cowboy" the menu attributes this dish to should give them a couple of days under his saddle to tenderize them before trying to chew them. Although the entree is meant for two, you can order a single portion of the parrillada, but don't bother. You can also order short ribs a la carte for $5.95, but since I couldn't chew my way through one piece on the mixed grill, a 14-ounce portion sounds like more exercise than jogging.

No. 5 -- Bife a caballo, strip steak with two fried eggs, $7.95. Two fried eggs do not compensate for thinness in a steak.

No. 6 -- Delmonico steak, 12 oz., $9.95. See prime rib.

Prime rib, pullman cut, 16 oz., $12.95. How such a thin rib steak could weigh a pound is a question that could have scientists scurrying to their laboratories. And why a request for rare prime rib brings a grilled and chewy piece of well-done rib steak is a question I might have asked the waiter -- had not a previous waiter already acted as if it were an imposition to admit that my rare steak was well done and to do something about it. Another one to skip.

Finally, there is a 12-ounce steak known as churrasco for $6.95, which turns out to be a lot of meat, very thick, with little flavor and dry texture, obviously a cut insufficiently marbled to recommend grilling. It is, however, plenty of meat for the money and not bad. r

To sum it up, the central and routine part of Las Pampas' menu -- the beef -- is erratic.One day, two steaks ordered rare came one rare and one medium; another day three rare orders came one rare, one medium and one well-done.

If a beef grill can't consistently serve acceptable grilled beef, what can it do?

It can serve kettles of wonderful homemade ssoups, particularly the lentil with greens and sausage (which the waiter described as chicken soup). The actual chicken soup, with chunks of meat and vegetables in a tomato broth, was only slightly less wonderful.

It can, apparently on alternate days, serve excellent french fries, crusty and highly seasoned, most noticeably with paprika and pepper. On other day, however, the french fries have been cold and tough, barely seasoned. And every day the salad is just a large bowl of iceberg lettuce with tomatoes, scallions and a large dose of vinegar.

Ordering the soup and chicken -- with, perhaps, a flan for dessert, though it is ordinary -- brings an excellent meal at modest price, particularly for Georgetown; add a pleasant Argentinian cabernet sauvignon for $7.50 a bottle, and Las Pampas is a Georgetown discovery. The service is so erratic that sometimes three waiters show up to serve your steak, and other times the waiter appears either distracted or uncomfortable communicating in English. But it somehow works, under the guise of ethnic charm. Las Pampas is fun, but be sure to go by the economy fare.