IN TOWN

City slicker Santa has traded his sleigh for a horse-drawn carriage and he'll be offering block-long rides on Friday from 1 to 5 and Saturday 11 to 3 starting at McLachlen National Bank, 11th and G streets NW. The Saturday rides will continue through December 21. Rides are $1 for adults, 50 cents for children 12 and under. For more information, 639-4011 . . . Mickey Mouse, backed by a U.S. Marine Corps color guard, will light the Vista International Hotel's 20- foot Christmas tree Friday at 4. The tree, decorated with dolls from around the world, is joined by Washington's largest wreath, a 22-foot, 780-pounder that hangs inside the Vista's 14-story atrium at 1400 M Street NW. Free. 429-1700.

IN MARYLAND

This weekend's Maryland Christmas Show at the Frederick Fairgrounds signals the official start of the shopping season. Quilts, toys, jewelry, pottery, baskets, dolls, folk art and more will be for sale on Friday through Sunday, 10 to 6. Adults $3; children six to 12, $1.50. 301/898-5466 . . . Nearby in Brunswick, Christmas 1890s-style returns to the Brunswick Museum this Saturday and Sunday with a wide array of Victorian Christmas decorations, stories and homemade food. Kids can visit with Santa on Saturday, 10 to noon, while their dads play with more than 300 pieces of model railrod trains on a one-third-mile track. Hours: 10 to 5 each day. Admission to the museum is $2 for adults; $1 children 6 to 12; free for five years and younger. Call 301/834-7100.

IN VIRGINIA

Square dancers can do their part to help needy kids at Christmas time this Sunday afternoon from 1 to 5. There'll be a Square and Round Dance to benefit the Marine Corps' Toys for Tots program in the T.C. Williams High School cafeteria, 3330 King Street, Alexandria. Dancing pairs are asked to bring a new child's toy or contribute at least $5 . . . The Northern Virginia Carvers will exhibit their abstract sculpture, ducks and decoys Saturday and Sunday, 10 to 6, at Marymount College, North Glebe Road and Old Dominion Drive, Arlington. Adults $1, children and parking are free.