Look out, Washington, Baltimore is joining the fray. Chambord, a magnificent townhouse drippig with chandeliers and garlanded with fireplaces, is a French restaurant as sophisticated and ambitious as any in Washington, with the luxurious sense of dining in a private home that cannot be matched here. In the lounge, a pianist is playing dinner music. The banquettes are as comfortable as sofas, the tables large and spaced with unfamiliar generosity. Velvets, silks, flowers, soft colors, the sum is regal. So is the service, informed and consummately attentive but unobtrusive. The details are inordinately rich, from very good imported house wines to outstanding tableware to dishes being presented with flowers and plumes garnishing them. The menu is undergoing changes, but in past experience the mussel soup has been a faintly lemony puree with a few mussels and shreds of vegetable and immortal flavor. They offered seconds, and nobody refused. The pates were stunningly presented and finely flavored, but no competition for the soup. Main dishes missed slightly, the trout being faintly fishy and blandly sauced, the veal clumsily butchered and oversalted, the rack of lamb being strong meat in a weak sauce, the texture considerably better than the flavor. But back to the details: each dish had a different starchy vegetable, each good, and all had excellent fresh broccoli with proper hollandaise, plus a very good Bibb lettuce salad. The wine list seemed endless in its choice of burgundies, and the bordeaux and California selections were no slouches. While prices were wide-ranging, there were some tempting bargains and a good number of choices under $10. The brie was ripe, and nicely served with fruit. The climax, though, is dessert, rolled up on a cart full of tarts, tortes, cheesecakes mousses - elaborately decorated with buttercream rosettes and chocolate cutouts. The house cake - crisp sweet chocolate biscuit layered with butter cream and Grand Marnier, chocolate-decorated - is a marvel, eclipsing uncommonly good tarts and tortes, even the tiny cookies and chocolate-covered orange peel that accompanies the coffee. With improvement in the main courses, Chambord would fulfill the palatial style it has undertaken.