Here are some October fests, fairs, fleas and shows, close to home:

Potomac's Our Lady of Mercy Church has its third annual ANTIQUES SHOW & FAIR Friday and Saturday, 11 to 9, and Sunday, 11 to 5. Admission is $2.50 at Kentsdale Drive and Bradley Boulevard.

A QUAKER BAZAAR at 2111 Florida Avenue NW features an antiques auction and has crafts for sale Saturday, 10 to 4. Admission free. The Potomac School in McLean has the fifth annual FALL FROLICS Saturday, 10:30 to 3:30, with rides, games, music, arts and crafts; an auction is at 2. Take Route 123 from the G.W. Parkway to a left on Potomac School Road. Eye Care, Inc., auctions off nearly 150 pieces of HAITIAN ART off at the Haitian Embassy Sunday, 4 to 9, in an effort to raise money for its medical work in the Third World. The Ambassador of Haiti hosts the auction at 2311 Massachusetts Avenue; $20 donation at the door may be applied to purchase. Call 789-2612.

Rockville Civic Center Park, at Baltimore Road and Edmonston Drive, hosts the 20th annual ANTIQUE & CLASSIC CAR SHOW 9:30 to 4 Saturday. Call 424-3000, ext. 203.

The Holy Redeemer fourth annual ART AUCTION in Kensington is Saturday with the exhibition at 7, auction at 8. Admission is $2.50 at 9715 Summit Avenue. Call 933- 5114.

Mount Vernon School's FUN FAIR & FLEA MARKET starts at 9, with entertainment 11 to 4. At 2601 Commonwealth Avenue in Alexandria.

In Northern Virginia, 75 families contribute to a YARD SALE at Montessori School Saturday 8 to 3 at 6820 Pacific Lane in Annandale. Call 256-9577.

And farther afield: ALDIE, VIRGINIA, celebrates the harvest season with a festival Saturday, 9 to 5, with crafts and fresh produce. On Route 50, 35 miles west of D.C.

In CRIGLERSVILLE, VIRGINIA, a fall festival of arts and crafts Saturday and Sunday has crafts and food for sale, and live country music in the afternoons. Free, 10 to 6 both days. Take U.S. 29 to Madison, then north on Route 231 to Banco, left on Route 770 to Criglersville and follow signs. Call 703/923-4244. Meanwhile, two miles south is an Apple Festival at Graves Mountain Lodge (call 703/923-4231) and a Mill Tour and Music Festival two miles north at Olive Mills Gallery in Banco (call 703/923-4328).

St. James Lutheran Church in UNIONBRIDGE, MARYLAND, invites all to the 100th anniversary tour of nine Victorian and century-old homes in that town. Cost is $7 for both Saturday (10 to 6) and Sunday (12:30 to 6). About an hour away: Take I-270-north to Route 15 north, then east on Route 26 and north on Route 75. Call 301/775-2040.