14670 Southlawn La., Rockville 424-7373 Hours: 11 a.m. to 10 p.m. Monday through Thursday; 4 to 11 p.m. Friday and Saturday; 4 to 9:30 p.m. Sunday. Prices: Most dinner entrees $7 to $13. Cards: American Express, Choice, MasterCard and Visa.

Sylvia's, a modest Italian restaurant in a part of Rockville known mainly for warehouses and auto repair specialists, has been demonstrating for several years that a place serving very good food at a fair price can thrive even in the unlikeliest of settings. Judging from the crowds at Sylvia's these days, that axiom is truer than ever.

But Sylvia's food may be wavering a bit lately. You can still eat well here, but only if you order carefully. And we noticed more quality control slip-ups recently than in the past.

For starters, the red pepper and anchovy appetizer remains a delight, a big platter of sweet pepper slices topped with whole anchovy strips, parsley and minced garlic, served in a bracing oil and vinegar dressing.

Spiedini, a layered combination of bread and melted cheese that's battered and fried, was light and free of excess oil, but it was cold in the middle.

Fried zucchini, sliced paper thin, had a properly delicate egg batter, but it was oilier than it should have been.

The white pizza also was too oily, despite its zippy flavor and chewy crust. The salad is a pretty mixture of vegetables, with a good, simple oil and vinegar dressing.

One of the biggest disappointments at Sylvia's lately is the bread. It's the genuine, thick-crusted Italian article, but with a rubbery texture, as though it had been heated in a microwave oven.

The shellfish remains excellent here. A nice way to sample it is in the seafood platter, a copper pan filled with calamari, shrimp, clams, mussels and crab legs, all sweet and tender, served on a bed of good, chewy linguine. To enjoy the seafood flavor best, have this dish with the white sauce, a gentle broth of seafood juices, garlic and parsley.

With the veal, too, simplicity is best. This is high quality meat, tender and fine-textured, and it needs only a light lemon sauce (veal piccata) to play it up. We made the mistake of ordering veal marsala, with a sauce far too sweet and boozy for the meat. Another mistake was chicken paesana, slices of breaded chicken breast in tomato sauce. The chunky, robust sauce was delightful, but the chicken was dry and the breading hopelessly soggy under all that liquid.

The tomato sauces have been excellent across the board, lively and fresh tasting. Even the linguine-tomato sauce side orders, generally an afterthought in restaurants, are worth eating. A good way to enjoy the tomato sauce is with the sausage and green peppers. Sylvia's version would have been a winner, except that the pleasantly peppery, anise-laced sausage was crumbly-dry.

The poorest dishes lately have been the casseroled pastas. The manicotti was soft and wet, and the lasagna, although tasty, was even mushier, collapsing at the touch of a fork and resting in a puddle of watery liquid at the bottom of the serving dish.

For dessert there are good, crisp-wrappered cannoli and formidable chocolate-coated tartufo ice cream balls.