Whether it's carving a pumpkin, showing off a costume, listening to a tale of terror or daring a visit to a haunted house, you've got more than a ghost of chance this weekend to prime yourself for Halloween night.

You can call a park service to get in touch with a Halloween activity in your neighborhood (best done on Friday). For Arlington County residents the number is 558-2700, 941- 5000 in Fairfax County and 699- 2407 for both Montgomery and Prince George's counties.

The following sampling of other activities should also help summon that Halloween spirit.

WASHINGTON GHOST STORIES -- Friday, 6:30 to 8 p.m., Saturday, 11 a.m. to 12:30 p.m., Rathskeller, Christian Heurich Mansion, 1307 New Hampshire Ave. NW. Storyteller Jean Alexander, a featured performer on National Public Radio, tells of Washington's ghostly past; Halloween treats served. Children must be accompanied by adults; not recommended for pre-school kids. $2 per person; $1.50 per person for families. 785- 2068.

HALLOWEEN PRE-TEEN DISCO AND PUMPKIN CARVING CONTEST -- Friday, 7 to 10 p.m., Ramsay Recreation Center, 5700 Sanger Ave., Alexandria. Kids ages five to 12 can enter a costume contest, play Halloween games and enter a monster mash dance contest; parents welcome. $2 per child. Saturday, 10:30 to noon, nature center, pumpkin carving contest; participants must provide own pumpkin, knife, spoon and any natural object with which to decorate. Prizes for the best in categories include: most unusal, most creative idea, most traditional, most scary and best parent-tot team. $1 entry fee. 838-4826 or 838-4829.

MURDER MANSION -- Friday-Thursday, 7 to 10 p.m., Von Baron House, 1201 N. Frederick Ave., Gaithersburg. Kids with cast- iron nerves can dare this old and eerie haunted house. Adults $2; children 12 and under, $1.50. 977-2856.

HAUNTED HYATTSVILLE GRAVEYARD -- Friday, 7 to 10; Saturday, 2 to 5 and 7 to 10, Prince George's Plaza Community Center, 6600 Adelphi Rd., Hyattsville. A graveyard open to all who dare enter; those under six may want to think twice. Adults $3; children six to 12, $2. 864-1611.

SPIRITS IN THE GLEN -- Friday, 7:30, Adventure Theater, Glen Echo Park, Glen Echo. Storyteller Sharon Butler weaves Halloween tales for families. $3. For reservations and more information, call 627- 3023.

OLD-FASHIONED HALLOWEEN -- Friday, 8 to 11 p.m.; Saturday, 6 to 10 p.m., Unitarian Church of Arlington, 4444 Arlington Blvd., Arlington. An old-fashioned Halloween party, face-painting clinic, games and haunted house. Adults $2; children $1; games a quarter.

PUMPKINS AND SCARECROWS -- Saturday, 10 to noon, Forest Heights Elementary School, 200 Talbert Dr., Forest Heights, Md. Bring a pumpkin and cut it down to size, for a prize. Also a scarecrow-making workshop; $1 per scarecrow. 248-1260.

HALLOWEEN PARTY -- Saturday, 10 to noon, Decatur Community Center, 5200 Pinewood Dr., Clinton. Magic show, games, costume parade and contest for kids 10 and under. $1. 297-4648.

FAMILY FALL FESTIVAL -- Saturday, 11 to 3, Chevy Chase Elementary School, 4015 Rosemary St., Chevy Chase. Haunted house, cider, pumpkins, moon bounce, facepainting. 652-0015.

SCARY STORIES -- Saturday, 11 a.m. and 1 p.m., Cheshire Cat Bookstore, 5512 Connecticut Ave. NW. Author Alvin Schwartz tells stories from his books to give you the creeps. The first show is for kids four to seven; the later show for children eight and up. 244-3956.

OLD POST OFFICE -- Saturday, 11:30 to 1, Halloween stories and a clown company that makes a Halloween face for you. Pavilion, 1100 Pennsylvania Ave. NW. 289-4224.

HALLOWEEN PARTY AND HAUNTED HOUSE -- Saturday, 1 to 3, Vienna Community Center, 120 Cherry St. SE, Vienna. Children aged six to 12 are invited to wear their Halloween costumes to a free party featuring carnival games, clowns and entertatainment. Saturday-Monday, 7 to 10 p.m., haunted house. Adults $2; children $1. 938-8000, ext. 277.

HALLOWEEN STORIES -- Saturday, 1:30, Twinbrook Library, Viers Mill Road and Meadow Hall Drive, Rockville. Listen to Halloween stories and see the Penny Theater perform "Hester"; recommended for children ages three to six. 279-1982

HALLOWEEN CARNIVAL -- Saturday, 2 to 3:30, Laurel Armory Community Center, 422 Montgomery St., Laurel. Children under 12 can enter costume and jack-o-latern contests and play games, see a magic show. 725-7800.

COSTUME CONTEST -- Sunday, 3 to 6, Lee District Park, 6601 Telegraph Rd., Rose Hill, Va. (take Beltway exit 2-S; park entrance is 21/2 miles on left). Children ages two to 12 can enter a costume contest, watch Halloween movies, walk down a haunted hallway and eat popcorn. Judging takes place for kids six and under from 3 to 4; ages 7 to 12 from 4:30 to 5:30. $1 per person. 922-9841.

HALLOWEEN MOVIES -- Sunday, 4 to 6, Seat Pleasant Activities Center, 5720 Addison Rd., Seat Pleasant, Md. Children nine and under can watch Halloween movies, play games, dance and eat candy. 773-6685.