What's more alone than "Home Alone"? It's "Camp Nowhere," in which a band of pre-teen-agers have the bright idea of escaping their pushy parents for the summer. While the parents contemplate various educational camps for their children ("Camp Microchippewa" is an option for the computer-conscious), the campers scrounge up enough money to rent some empty cabins and hire Dennis Van Welker (Christopher Lloyd) to pretend to be an adult. For Dennis, a good-natured, down-and-out casualty of the 60's, this is not an easy assignment.

If "Camp Nowhere" stuck to the predictable high jinks -- buying toys, having pie fights, jumping off the roof onto mattresses -- it would be about as welcome as poison ivy. Fortunately, there's a funny screenplay (by Andrew Kurtzman and Eliot Wald, two "Saturday Night Live" writers), good-humored direction by Jonathan Prince, and a nice young cast. Most of the actors have television experience, and they bring a sturdy, no-frills professionalism to their roles.

Best of all, this film provides a good opportunity for Mr. Lloyd, an actor who has figured appealingly in many child-oriented hits (the "Back to the Future" and "Addams Family" films; "Who Framed Roger Rabbit"). This time, Mr. Lloyd gets to play a cheerful, eager burnout whose hippie past is never far behind him. Reading the label on a medicine bottle prescribed for Morris (Mud) Himmel (Jonathan Jackson), the campers' ringleader, he advises four pills every hour. But the label says one pill every four hours. "Ooh!" sighs Dennis. "Not the first time that mistake's gotten me in trouble."

Dennis will try anything to fool a bill collector (M. Emmet Walsh), the local law officer (Tom Wilson, the bully of the "Back to the Future" series) or the campers' parents. This is handy, since some of those parents think they've sent their children to military camp; some think it's diet, acting ("Shakespeare Hamlet") or computer camp ("Binary Pines"), respectively.

The film's piece de resistance comes when the parents insist on visiting, and their children stage a complicated four-tiered visiting day. This sequence is long and amusing enough to make up for the film's slower stages. Best moment: when a sign that reads "To Saigon" for mock military maneuvers is changed to read "Miss Saigon" when the Broadway-minded parents arrive.

Smaller children may miss jokes like this, but they should enjoy the overall good humor on display. And for adults in the audience, Mr. Lloyd is a definite bonus. Trying to woo a pretty local doctor (Wendy Makkena), for instance, he invites her to dinner, pretending to be Mud's loving father. Then Mud falls asleep, and the boy becomes an inconvenient presence. Lovingly, Dennis lifts Mud, opens the cabin door and deposits him in what is supposedly a bedroom -- and is actually the back porch.

Later on, confronted about this in broad daylight by the doctor, Dennis looks suitably aghast. He surveys the porch, thinks fast, and delivers the only feasible comeback: "Good lord, there must've been a tornado!"

"Camp Nowhere" is rated PG (Parental guidance suggested). It includes mildly off-color language and some smooching in its last reel. CAMP NOWHERE Directed by Jonathan Prince; written by Andrew Kurtzman and Eliot Wald; director of photography, Sandi Sissel; edited by John Poll; music by David Lawrence; production designer, Rusty Smith; produced by Michael Peyser; released by Buena Vista Pictures. Running time: 96 minutes. This film is rated PG. WITH: Christopher Lloyd (Dennis Van Welker), Jonathan Jackson (Morris Himmel), Tom Wilson (Lieut. Eliot Hendricks), Wendy Makkena (Dr. Celeste Dunbar) and M. Emmet Walsh (T. R. Polk)

Photo: Members of the young cast frolic in a scene from "Camp Nowhere." (Suzanne Tanner/Hollywood Pictures)