For all those out there who can't get enough of Prince, Under the Cherry Moon may be just the antidote.

Labyrinth, a fabulous film about a young girl's journey into womanhood that uses futuristic technology to illuminate a mythic-style tale, is in many ways a remarkable achievement.

THE most irresistible thing about the characters in Ruthless People, a conspicuously overconsuming, Beverly Hills update of O. Henry's classic Ransom of Red Chief, is that they all try with such earnestness to live up to their ruthless reputations. It also has a uniformly splendid cast of comic actors - the best to be seen outside of any recent Blake Edwards movie. Its screenplay, by the newcomer Dale Launer, is packed with wonderfully vulgar, tasteless lines that perfectly reflect the sensibilities of Sam and Barbara Stone.

Still another, thoroughly depressing demonstration of the extent to which television now dictates the style and the manners of so many of the movies we see in theaters.

Even as sequels go in this era of movie mega-series, The Karate Kid Part II peters out faster than most.

Though publicized as a breakthrough into adult comedy for Mr. Reitman (''National Lampoon's Animal House,'' ''Meatballs,'' ''Ghostbusters''), this new film is less a true adult comedy than a teen-age comedy populated by adults who are functioning in an adult world.

The film is a good-natured potpourri of gags, funny bits, populist sentiment and anti-intellectualism.

Mr. Brickman, who directed the film and wrote the screenplay (with Thomas Baum), has a real gift for eccentric comedy and characters. The Manhattan Project, with its vaguely populist leanings, isn't crazy enough. Mr. Brickman fails to make big issues comprehensible. He just makes them small.

NEIL JORDAN'S Mona Lisa is classy kitsch. It's as smooth and distinctive (and, ultimately, as insubstantial) as the old Nat (King) Cole recording of the song, which gives the film its title and a lot of its mood. It's also got high style, so you needn't hate yourself for liking it.

In this film [Hughes] has created a character who is every teen-ager's fantasy, but in the process he has lost some of the authenticity of his other films - leaving several slow transitions or awkward moments.

Though the language is vulgar, the macho posturing absurd and some of the plotting inscrutable, Raw Deal has a kind of seemliness to it. It delivers every punch it promises.

The outcome is pretty predictable, but it's done well, and the actors do a good job of transforming general types into individuals whom we grow to like. It is also hard to resist Jinx, the funny little computer responsible for all the trouble.

The director, Tobe Hooper, who honed his scary craft on such films as ''The Texas Chain Saw Massacre'' and ''Poltergeist,'' knows how to construct a horror film so it builds to a screaming pitch. He shoots many of his images from below, to give the view a child might have, and deftly manipulates the audience to feel the growing menace. He is helped by an excellent cast.

All this may be enough to keep 3- to 7-year-olds entertained for an hour and a half on a hot summer's day, and there is certainly nothing in this sanitized fairy tale that will frighten or alarm them unduly. Unlike the great Disney classics, however, there is also nothing that will move them - and there are very few bones of wit thrown to the poor parents who will have to sit through the film with children of this age group.

Most of the possibilities for humor or tension, either sexual or dramatic, are badly botched by the flat performances of the other lead actors and the consistent bad timing of the director - everything misfires or misconnects, leaving too many long, dead moments that prove that even an adventure film with lots of running and shooting can be boring.

It possesses high points you simply don't find in lesser if more consistently funny movies.

All the people and places in Demons seem imported. The dialogue is spoken in colloquial American and matches the lip movements, but it sounds dubbed. Nonetheless, there are some apt observations.

A disturbing movie from many points of view: disturbing for the violence it portrays, the ideas it represents and the large number of people who will undoubtedly go to see it and cheer on its dangerous hero.

The excitement is switched off on landing. Once Top Gun, which opens today at Loews Astor Plaza and other theaters, gets back to earth, the master of the skies is as clunky as a big land-bound bird.

A cheerful, inoffensive fantasy in which such attractive live actors as Steve Guttenberg and Ally Sheedy play second fiddle to machinery that, in this case, means No. 5, designed by Syd Mead and engineered and realized by Eric Allard.

The karate blows sound good but never seem to make contact. But then nothing else makes contact either. The advice from this corner: Retreat.

Blue City is full of unbelievable, ineptly staged action sequences. It's most offensive, however, for its dialogue, and for the frivolous way it debases the shock value of obscene words. If, in 10 years, we wind up with an utterly colorless language, movies like this will have been at least partly to blame.

Jo Jo Dancer is a far from great movie. However, there's something revivifying about seeing Mr. Pryor take this flyer in writing, directing and acting in his own work.

It's full of film knowledge and is amazingly elaborate for a low-budget movie. The only problem is that it's not funny. One smiles at the inspiration of the jokes, though not at their execution.

Three Men and a Cradle is almost totally charmless. It's funny in the way of someone who, in attempting to explain a joke, thoroughly destroys the humor, which, I assume, is mostly the fault of Coline Serreau, who wrote and directed it.

HOW did Eight Million Ways to Die commit suicide? Let us count the ways.

The main characters tend to be either grotesques or stereotypes, who keep getting into incoherent arguments, composed largely of variations on America's favorite epithet...For a movie with pretensions to laying out political realities, the colorful Salvador is black and white.