Open for lunch Monday through Friday, 11:30 a.m. to 3 p.m.; for dinner daily, 5 to 10 p.m. AE, MC, V. Reservations. Prices: Main courses at lunch, $4.50 to $7; main courses at dinner, $4.50 to $12, averaging $6 to $7. Appetizers, large enough for two, average $5.

This would seem a marriage made in heaven. Szechuan East, with a downtown location, needed new life. Siam Inn, in Wheaton, was a very good Thai restaurant needing a more central location. So it branched into the old Szechuan East and hung its trademark: silk parasols suspended upside down from the ceiling.

Except for some intricate cut-paper wall hangings and waitresses in gorgeous Thai silk tunics with long skirts, the Siam Inn looks much the same as the old Szechuan East, its small room tightly furnished with white-clothed tables against yellow ocher walls. It still smells of disinfectant, though garlic and pepper dominate at the tables. Its service has improved immeasurably, however, with waitresses who are obviously eager for you to enjoy your meal and to return. Whatever they can do towards that end they do, explaining dishes and pouring water and bringing a new dessert for you to taste or the dinner menu to entice you back if you have come for lunch.

In relation to the Siam Inn's origianl branch, at least as of my last visit a year ago, there have been three significant changes. On the positive side, the surroundings are more decorative. On the negative side, though, the prices are much higher, and the cooking is much less painstaking.

Thai food is similar in style to Chinese cooking, with ingredients usually cut into small pieces and stir-fried, but the seasonings are likely to be fiery and the sauces unthickened but plentiful. The menus we see in Washington consist largely of chicken, beef, pork or shrimp with hot pepper and onion, an Asian variety of basil with pepper, ginger and mushroom or garlic and white pepper. Thus, seemingly extensive menus break down into a few themes. The greatest variety is in appetizers, and locally they tend to be the best dishes.

At the downtown Siam Inn, the appetizers are better than ever. The spring rolls are wrapped in a very thin and crisp dough, filled with a highly perfumed meat and transparent noodle stuffing. The starchy red sauce that accompanies the Siam Inn Chicken, perhaps the best dish in the house and unfortunately not available at lunch. Four pieces of chicken are molded around a bone with a stuffing of black mushrooms and crabmeat, heavy with garlic. Dipped into a light batter and deep fried, they are a delicious combination of flavors and textures. Satays, small bits of meat flavored here with curry and grilled on skewers, are popular; though the meat is a coarse cut, the blend of flavors with the slightly sweet peanut dipping sauce is excellent. Most of the rest of the appetizers are cold meats with or without noodles, highly seasoned with lemon and hot pepper. They are unusual and very good if you like such intense seasoning -- and are forewarned that the meat may be, unexpectedly, tripe. Finally, among the appetizers are intriguing and also fiery soups based on coconut milk or the sweet perfume of lemon grass.

My favorite main dish at the old Siam Inn has been fried ox tongue with garlic and pepper, the meat tender with a slightly crisped surface and highly aromatic from the fried chopped garlic and pepper. It was a severe disappointment at the downtown branch, for the tongue was mushy and greasy, with a tough surface that had been fried too long, and the seasoning lacked the intensity and fragrance of the old days. It was also more than twice the price, which I would have gladly paid for the old quality at a downtown location. Chicken with garlic and pepper was also dry, overcooked and greasy, not more satisfactory even though it, inexplicably, cost a dollar less than the tongue at dinner. These criticisms apply to most of my entrees at the Siam Inn: greasy and lacking the moist fresh texture of careful stir-frying, with ginger and garlic and soy sauce, but lacking the wonderful touch of the old days.

Six or seven dollars is no longer a high price for a main course at dinner, but the Siam Inn is not the astonishing bargain that it once was, and merits less forgiveness for a soupy beef Thai-style with neither a lot of meat nor a lot of character. Surprisingly, a few of the fried rice and noodle dishes are cheaper at dinner than at lunch, but in general lunch dishes are 75 cents to $1 cheaper. Still, dinner is the best time to try the Siam Inn. It is prettier with tablecloths and candlelight. It is quieter. And the menu is more extensive. Dinner warrants lingering over a bottle of wine; the very short wine list is a nice choice of California boutique wines averaging $9. Or try the "beer or the month" (approximately enough, a Thai beer when I visited).

Siam Inn is a change of pace for the neighborhood, and takes the pains to garnish food prettily, often with elaborately carved and fringed slices of cucumber centered with a cherry, sometimes with fresh basil leaves. Though it is not as good as it was in the old days, it is more accessible to more people, and one of the few downtown restaurants open Sunday.