DREAMING OF A WHITE HOUSE CHRISTMAS

Not everyone has the room for an 18 1/2-foot Christmas tree, but then again, not everyone lives in the White House. You can see the decorated house and its holiday evergreen (studded with 1,500 ornaments) on tours from 10 to noon Saturday -- or by candlelight from 6 to 8 Monday, Tuesday and Wednesday. (It'll also be open 10 to noon Tuesday and Wednesday). Free. Call 472-3669 or 485-9673 for information.

SURELY SULLY

Historic Sully shines with an 18th-century holiday illumination at 4 Sunday with cannon firings, tours of the federal-period estate, caroling by the Music of Turkey Run and storytelling. It all ends brightly with fireworks at 6:30. It's $4 for adults; $2 for kids 3 to 15. Take U.S. 50 west to Rte. 28 north (Sully Road) and follow the signs. 437-1794.

NEW YEAR'S DOINGS

Usher in the New Year at the following hot spots (or check the listings in "Sounds" inside for nightclub plans and other New Year's activities).

In town, the Old Post Office Pavilion is the place for free entertainment that begins at 9 with shows on two stages. At 14th Street and Western Plaza starting at 9, singers Willie Jolley and Gloria Hightower perform, followed by R&B band Stratus at 10:10 and singer Nona Hendryx at 11:10. At 10th and Pennsylvania, hear vibraphonist Roy Ayers at 9, keyboardist Dave Robbins, the All-Stars at 10 and D.C.'s own Stacy Lattisaw at 11. After the music, the Pavilion's countdown will be led by Mayor Marion Barry as a lighted '88 "Love" stamp is lowered for the magic moment. Take Metro to Federal Triangle or Metro Center; trains run until 2 a.m. 673-7660.

Baltimore's Inner Harbor glows beginning at 11:30 p.m. Thursday with the tap-dancing Manhattan Rhythm Kings, TV personality Harry Anderson and fireworks at midnight. Before you head to the harbor, stop by at the "family parties" at the Baltimore Convention Center, where entertainment includes the rock 'n' rollin' Mahoney Brothers and pop group The Look. It's $6. 301/837-INFO.

Leesburg welcomes the New Year family-style with blues singer John Jackson, rock band Raydio Flash Cab, Doc Dikeman's Dixieland Band and others at 8 Thursday around downtown Leesburg (call 703/777-0519 for locations). The evening will close with fireworks. It's $3.

ALTAR-NATIVES

Ten churches and a synagogue open their doors for a free self-guided tour 6:30 to 9:30 Sunday in historic Frederick. Begin at Trunk Hall of the Evangelical Lutheran Church, 35 East Church St., where you can pick up a free map and refreshments. Free. Call 301/663-8687.

COSMIC LEAPS

If you or yours got a telescope for Christmas, or whenever, Goddard Space Flight Center is the place to be this Sunday from 1 to 4, for a workshop on the how-tos of telescopes, including what to look for once you've assembled and learned how to operate them. The program is free at the Goddard Space Flight Center off Rte. 193 at Soil Conservation Road, outside Greenbelt. Call 286-8981 for information.

GALLERY SOUNDS

Unwind Sunday night at the National Gallery of Art when pianist Francis Conlon performs works by Haydn, Barber, Ravel and Liszt at 7 in the East Garden Court. Free. 737-4215.

REEL TO REEL

Picking films for the entire family is difficult; let the Smithsonian do it for you this week in its "Films for the Young and Old" series being shown in conjunction with the "Generations" exhibition. Screenings of the six films, which include "Children, Enfants, Ninåos," "Made in China" and "Family Album," are at the Lecture Hall, S. Dillon Ripley Center, 1100 Jefferson Dr. SW (on the Mall in the new underground museum) from 11 to 3:15 Saturday through Thursday. 357-2700.

WATTS HAPPENING

If you've already seen the Pageant of Peace on the Ellipse, there are always these other bright spots:

The Festival of Lights at the Mormon Temple is 80,000 lights strong -- with a live manger scene and a Christmas tree exhibit. This weekend, there'll also be music in the Visitor's Center at 6:30 Friday and Sunday and 6:30 and 7:30 Saturday. It's free at 9900 Stoneybrook Dr. in Kensington. 587-0144.

At R. M. Watkins Regional Park in Largo, the trees are lit with 30,000 lights. There'll also be a lighted train station and carousel and an illuminated Santa with reindeer. It's free; take the Beltway to Rte. 214 and follow the signs. 952-3560.

A LITTLE THEATER

The spotlight is on children's theater this weekend.

The Capital Children's Museum brings the fairy tale "Babes in Toyland" to life via Glen Echo's Puppet Company. Showtimes are at 1 and 2:30 Saturday and Sunday at the museum, 800 Third St. NE. It's $6 for the show and admission to the museum; $2.50 for the show alone. Call 543-8600.

The Montgomery Playhouse's "A Tail of a King" stars children -- elementary students to high schoolers -- who are all members of the Playhouse's summer theater camp. Showtimes of the play, which includes jazz, boogie, rap and show tunes, are 2:30 and 7:30 Saturday and Sunday at the playhouse, 1201 Quince Orchard Blvd. in Gaithersburg. For other showtimes, call 948-6669.

EVERGREENS

You don't need a green thumb to hear the Greenville (S.C.) Singing Christmas Tree at the Kennedy Center Concert Hall at 3 and 7 Sunday. The singers hold forth with holiday songs while standing atop a 26-foot structure covered in greenery. The concert will end with a sing-along. Tickets are $5 at the box office. 254-2700.

Tickets are still available for performances of the Washington Ballet's "Nutcracker" at the Lisner Auditorium. Showtimes are 2 and 7 Saturday (and Tuesday, Wednesday and Thursday) and 1 and 5 Sunday. Tickets are $14 to $16.50 via TicketCenter at 432-0200. Information: 362-3606.