Whimsy and a bit of cheer liven the latest fantasies

The latest fantasies are reasonably lighthearted, and I think that's a good sign. No dark ditherings like ''The Exorcist'' or ''The Omen'' here. Twilight Zone - the Movie has plenty of cheap thrills, but spices the action with whimsy and even a bit of cheer. And the inevitable ''Superman III'' turns out to be a comedy, complete with Richard Pryor in a major role.

As an old fan of the ''Twilight Zone'' TV series, I was pleased to see its format - and some of its stories - borrowed for a four-part ''anthology film,'' with the ingenious Steven Spielberg behind it. I was less pleased to learn that some of today's most overrated young filmmakers were also aboard the project. The result is full of surprises - beginning with the fact that Spielberg's contribution is the worst part of the movie.

The hero for his segment is a mysterious old man (played by the unique Scatman Crothers) living in a retirement home. Despite the gloomy moods of his elderly neighbors, he refuses to give up his love of life - and even shares it one magical night, literally turning his fellow pensioners into children.

It's a well-meaning story, but Spielberg tells it raggedly, with awkward shots and lumpy transitions. Amazingly, the wizard of ''E.T.'' and ''Close Encounters of the Third Kind'' doesn't even coax smooth performances from the children in the cast, who mug and overplay as archly as most of the grown-up performers. It's a real disappointment; maybe Spielberg was preoccupied with his next full-length film, a remake of the romantic ghost story ''A Guy Named Joe.''

Turning to the successful side of ''Twilight Zone,'' the last episode is a stunner by George Miller, the Australian director known to Americans for ''The Road Warrior'' and its much better predecessor, ''Mad Max.'' The setting is an airplane in a storm, and the star is John Lithgow as a panicky passenger. When he spots a monster on the wing, fiendishly sabotaging the plane, he gets more panicky yet - but everyone ignores him, figuring it's all a figment of his hypercharged imagination. The pace is relentless, the performances excellent, the editing sharp and crisp. In all, it's the best work Miller has given us so far.

The other episodes fall between these extremes. Joe Dante tells the classic story of a little boy with awesome powers he can't understand or control. Except for the gifted Kathleen Quinlan, most of the performers act much too broadly; but the yarn is redeemed by Dante's ingenious use of space, architecture, and menacing TV images. Visually, it's a treat, with some terrific Sally Cruikshank cartooning as a bonus.

Finally, the episode by John Landis (who also made the frivolous ''frame-tale'' that opens and closes the film) is a moralizing fable about a bigot trapped in a punishment that suits his crime. It's typical ''Twilight Zone'' fare in the old Rod Serling manner, but handled with little inspiration.

By contrast with the short ''Zone'' exercises, Superman III is a full-fledged epic. Yet it's smaller in scale than the earlier ''Superman'' pictures, and seems quite happy with its modest dimensions - a nice change of pace from the blockbusters that spawned it.

Richard Pryor plays a computer whiz helping a crooked magnate corner the world oil market. Superman, played as always by Christopher Reeve, foils him while also (as Clark Kent) courting Lana Lang, an old high school flame. The director, Richard Lester, sets the tone in the opening sequence, with a series of throwaway sight gags. And the mood stays light much of the way, except for a bout with kryptonite and a heavily symbolic scene wherein Superman literally wrestles with his ''secret identity'' - an intrusion on the fun of the movie, although it gives Reeve a chance to do some real acting for a change.

I talked with the ''Superman'' impresario, producer Alexander Salkind, in New York recently. He told me the ''Superman'' formula is set for good, as far as he's concerned, since audiences now have strong expectations of the series. This being the case, I give him credit - along with director Lester, a comedy veteran - for using humor in ''Superman III'' to leaven what could have been a most repetitious experience.

Meanwhile, what other tricks has Salkind up his sleeve? Instead of ''Superman IV,'' his next outing will be ''Supergirl'' - not a sop to feminists, he insists , but a fresh project with a personality all its own.

And then another kind of hero who wears a funny suit: ''Santa Claus,'' with an all-star cast and a colossal budget. Salkind says it will be the family-film adventure-comedy-romance of all time. Could he be right? Stay tuned. The mercurial Bob Dylan

Bob Dylan must be the most mercurial musician of his generation. He began as a folk singer inspired by Woody Guthrie. Later he turned to protest songs, love songs, rock, country music, and even his own brand of gospel, making each genre his own before moving on to fresher fields.

So there's a special fascination in the idea of glimpsing Dylan at a fairly early, and very formative, stage - 1965, to be exact, when his ''Subterranean Homesick Blues'' had just made a splash, and he was on the verge of switching from his previous folksy image to a new, hard-rocking persona.

''Don't Look Back,'' a biting documentary by D.A. Pennebaker, was shot on- and offstage during Dylan's last solo concert tour, before he started performing with an electrified backup group. About to be reissued after more than 10 years out of distribution, it's a grainy and unsentimental picture that captures its subject with all rough edges exposed.

Sometimes funny and sometimes unsettling, it's a particularly hard-nosed example of cinema verite filmmaking as well as a gritty record of what Dylan was like at a key moment of his career. Also included are snatches of such classic songs as ''Don't Think Twice, It's All Right'' and ''It's All Over Now, Baby Blue.'' In all, a worthy film that fully deserves another look after all these years.