While several of the museums on the Mall have cafeterias, including the National Gallery of Art and the Air and Space, Natural History and American History museums, they are likely to be packed during the festivities.

The pavilions at the District's "Main Street Millennium" celebration on Constitution Avenue between 10th and 14th streets NW will feature food by area restaurants from 11 to midnight Friday and 11 to 6 Saturday. And the sidewalk concessionaires will be around. For those who'd like something more substantial, here are some restaurants in the vicinity that will be open over the weekend.AMERICA--In Union Station at 50 Massachusetts Ave. NE (Metro: Union Station). 202/682-9555. Open Friday 11:30 to 4, Saturday and Sunday from 11:30 a.m. on. Casual menu of sandwiches, entrees and "regional specialities."

AMERICAN GRILL--In Loews L'Enfant Plaza Hotel, 480 L'Enfant Plaza SW (Metro: L'Enfant Plaza). 202/484-1000. Open daily from 6:30 on. Nice, broad family fare.

AUSTIN GRILL--750 E St. NW (Metro: Gallery Place/Chinatown). 202/393-3776. Open Friday 11 to 3, Saturday and Sunday from 11 on. Good Tex-Mex food, excellent chips and salsa, funky atmosphere, great music.

B. SMITH'S--In Union Station at 50 Massachusetts Ave. NE (Metro: Union Station). 202/289-6188. Opens Friday at 5, Saturday at noon and Sunday at 11:30. Updated southern fare with both soul and smarts.

BERTOLINI'S--801 Pennsylvania Ave. NW (Metro: Archives/Navy Memorial). 202/638-2140. Open Friday 11:30 to 8, closed Saturday, open Sunday 11:30 to 9. Modern-Italian yuppie magnet.

BIS--In Hotel George, 15 E St. NW (Metro: Union Station). 202/661-2700. Open Friday, fixed-price only after 5:30; Saturday 11:30 to 4:30; Sunday from 11:30 on. Classic French bistro fare in large portions and upscale atmosphere.

CAFE ATLANTICO--405 Eighth St. NW (Metro: Archives/Navy Memorial). 202/393-0812. Friday, fixed-priced dinner only after 5; Saturday and Sunday after 5. Quirky and satisfying Mediterranean fare.

CAPITAL GRILLE--601 Pennsylvania Ave. NW (Metro: Archives/Navy Memorial). 202/737-6200. Open Friday 11:30 to 3, dinner seatings at 5, 8 and 11 only; Saturday and Sunday from 5 on. Expense-account steakhouse with opportunities for celebrity sightings.

CHRISTOPHER MARK'S--1301 Pennsylvania Ave. NW (Metro: Federal Triangle). 202/628-5939. Open Friday and Saturday from 11:30, Sunday at 4. Upscale surf 'n' turf but kid-friendly.

CORNER BAKERY--In the National Press Building at 14th and F streets NW (Metro: Metro Center). 202/662-7400. Open Friday 9 to 5, Saturday 10 to 4, Sunday 10 to 3. Gourmet salads and sandwiches.

LES HALLES--1201 Pennsylvania Ave. NW (Metro: Federal Triangle). 202/347-6848. Open daily from 11:30. Franco-American steakhouse with the atmosphere of a French cafe.

HARD ROCK CAFE--999 E St. NW (Metro: Gallery Place/Chinatown). 202/737-7625. Open Friday lunch only 11 to 3, Saturday and Sunday from 11 on. Hamburgers, barbecue, nachos.

NATIONAL PLACE--1331 Pennsylvania Ave. NW (Metro: Metro Center). Food court open Friday noon to 5, closed Saturday, open Sunday noon to 5.

OCCIDENTAL GRILL--In the Willard Hotel at 15th and Pennsylvania NW (Metro: Metro Center). 202/783-1475. Opens Friday for fixed-price only at 5, seatings at 7:30 and 10. Saturday at 5 and Sunday from noon on. Modern-eclectic American fare with casual in-crowd atmosphere and good views.

OLD EBBITT GRILL--675 15th St. NW (Metro: Metro Center). 202/347-4801. Open Friday 7 to 5, Saturday and Sunday from 9:30 on. Tavern fare made modern American; signature chili and oyster bar.

OLD POST OFFICE PAVILION--12th Street and Pennsylvania Avenue NW (Metro: Federal Triangle). Food court open Friday 10 to 5, closed Saturday, open Sunday noon to 6.

PALOMINO EURO BISTRO--In the Ronald Reagan International Trade Center at 13th and Pennsylvania Ave. NW (Metro: Federal Triangle). 202/842-9800. Cafe opens Friday at 11:30, dining room opens Saturday at 5, Sunday at noon. Mod-California fare, from pizzas to rotisserie chickens.

PLANET HOLLYWOOD--1101 Pennsylvania Ave. NW (Metro: Federal Triangle). 202/783-7827. Open Friday and Saturday from 11 to 7, Sunday from 11 to 10:30. Pub-plus fare.

TGI FRIDAY'S--12th and Pennsylvania NW (Metro: Federal Triangle). 202/628-8443. Open Friday at noon, Saturday and Sunday from 11 on. Familiar family franchise with reliable and fairly varied fare.

UNION STATION--50 Massachusetts Ave. NW (Metro: Union Station). Food court open Friday 10 to 6, closed Saturday, open Sunday noon to 6.