The first thing you hear is a fiendish, deep- throated cackle rising from the darkness. Then the spotlight picks out a green, wart- studded face.

Meet the ghost of Canterville Hall, both fearsome and comical, able to instill just the right amount of hair-raising fear without scaring the little ones out of their seats.

The ghost is just one of many apparitions at Adventure Theater, a weekend performance playground for children and those who wish they still were. The theater is at Maryland's Glen Echo Park, where thousands once rode the roller coaster, were fooled in the House of Mirrors or took a dip in the Crystal Pool. It's now a cultural center.

Adventure Theater has had a long time to get its act together. The oldest such group in the area, it started in 1952 under the auspices of the Montgomery County Community Arts Association as a group of adult amateurs putting on plays for children. They've had to move to different stages over the years, but they're still volunteer performers putting on first-rate productions that you don't have to be a child to enjoy.

"The ghost scared me," said 46-year-old Delle Whittaker who came sans children. "I was kind of reliving my childhood."

The production that Whittaker and a hundred others paid $3 to see last Saturday afternoon is one of a number put on throughout the year. Others in the next few months will be "Rikki Tikki Tavi and Other Tales by Kipling," "The Pied Piper" and "Winnie the Pooh."

It is as much of an adventure for the performers as for the audience. Marlie Griffin, who for most of the week is a student at Walt Whitman High, has been caught up in the demanding world of drama for the last six weeks. But it's worth it, said Griffin, who has been acting for the last eight years. "I want to be an actress."

Not all the members of the cast aspire to show biz. "I want to be a psychiatrist," said 13-year-old Michael Wartofsky, who recently played Iago in "Othello" at the Folger Theater. "It's not easy to get parts," added Tiffany Garfinkle, who plays Wartofsky's twin and wants to be a pediatrician. "A lot of people try out."

The star of the show, Al Rupel, plays Sir Simon the ghost of Canterville Hall, an English estate. In an effort to rid the house of an unwanted American family, the ghost tries various scare tactics; eventually he learns that frightening people is not nice and returns to the realm of the dead.

The audience, which held as many children as adults, applauded the decision.

For the children, one of the best parts of the show came after the performance. The players came out front to receive congratulations and autograph programs for star- struck children.

"I think this show is particularily intriguing for children," said Al Rupel, who left his ghost mask backstage. "Especially when mom or dad is close enough to cling to."

THE GHOST OF CANTERVILLE HALL -- Saturdays and Sundays at 1:30 and 3:30 at Glen Echo's Adventure Theater through April 25. Tickets are $3 with group rates available. For reservations, call 320-5331 between 10 and 2.