A "Trick o' Treat Trot," sponsored by the Arlington YMCA and Junior League of Northern Virginia, will take place Sunday. A one-mile "fun run" is scheduled for 8:30 a.m. and a 10K run begins at 9 a.m. Runners are encouraged to wear costumes for the run. Breakfast, T-shirts and pumpkins will be given to all participants. Registration fees are $4 for the fun run and $8 for the 10K race. The proceeds will go toward literature and teaching videos for a "Fitness for Life for Children" program to be instituted soon in Arlington County schools. The race will begin and end at the Arlington County YMCA at 3422 N. 13th St., Arlington. For information, call the YMCA at 525-5420.

The Internal Revenue Service has a new toll-free telephone number available for Virginians to request federal tax forms and publications. The number, 1-800-424-FORM (3676), is open Monday through Friday from 8:15 a.m. to 4:30 p.m. Richmond residents can call 309-1052 during the same hours. These numbers are for forms and publications only, and are part of a new centralized inventory and distribution system designed to service form requests in a more efficient, economical manner. Orders from Virginians will be processed within 24 hours of receipt.

Callers needing tax information should call 1-800-424-1040; Richmond residents may call 649-2361.

Falls Church High School will sponsor the Campbell Classic 10K Race and Field Day on Saturday at the school, which is off Rte. 50 at 7521 Jaguar Trail, Falls Church. The race, which begins at 8 a.m., is in honor of Bruce Campbell, a 35-year mathematics teacher at the high school.

The registration fees are $10 for the 10K race, $4 for the fun run and walk race and $1 for the bike contest. For further information, call 573-4900.

The second annual Century 21-Easter Seal Volleyball Challenge will take place Sunday at Arlington's Thomas Jefferson Recreation Center. Novices to experts are welcome to play, and all proceeds will go toward services for physically handicapped children and adults in Northern Virginia. Trophies and prizes will be presented to participating teams.

Those interested in registering a team should call the 24-hour Volleyball Hotline at 522-2777.