'Ghostbusters': fantasy and zaniness done well; GHOSTBUSTERS. Produced and directed by Ivan Reitman. Original screenplay by Dan Aykroyd and Harold Ramis. Columbia Pictures; COALFIELDS. Directed by Bill Brand; STREETS OF FIRE, a rock & roll fable. Directed by Walter Hill. Universal-RKO.

At the beginning, we're in a dank parapsychology lab. Bill Murray is running a cheerfully unethical experiment, aimed mostly at getting a date with his subject. His partners want to investigate an uproar at the library, where spooks are messing up the card catalog.

At the climax, we're teetering from the edge of a blasted-out penthouse. Our heroes, with ''unlicensed nuclear accelerators'' strapped to their backs, are valiantly rescuing New York from a giant advertising figure made of marshmallow and somehow mixed up with ancient Sumeria.

And that's ''Ghostbusters'' in a nutshell. It starts with the sort of lowbrow , smart-aleck farce you'd expect from Murray and Dan Aykroyd, who star along with Harold Ramis and Sigourney Weaver. It ends with the wildest explosion of plot twists and visual effects this side of Steven Spielberg's fantasy factory. The treat of this ambitious comedy is that it values flamboyant imagination as well as earthy (sometimes coarse) humor. If the Three Stooges met ''The Exorcist ,'' this is what it would be like.

It's interesting that other current hits, like ''Gremlins'' and the ''Indiana Jones'' epic, also make a point of blending humor and horror, often in the same scene and even the same image. ''Ghostbusters'' puts the accent on laughs rather than shivers, of course, given the comedy credentials of its writers (Ackroyd and Ramis) and its stars. But the science-fantasy element is played for all it's worth, too, actually stealing the farce's thunder now and then. Credit goes largely to Richard Edlund's extravagant camera effects, and to the screenplay's knack for pushing outlandish ideas a big step farther than expected.

In both the funny and the (mildly) scary moments, the cast does itself proud. I've never been a fan of Aykroyd or Murray, but I enjoyed seeing them as restrained as they are here - hamming it up in the big scenes, true, but also pulling off sly jokes with small gestures and changes of expression. Ramis makes a nicely deadpan foil for them, and Sigourney Weaver has a great time with a role that's both playfully romantic and wackily demonic. A slew of fine supporting players also deserve special nods: Rick Moranis as the world's worst party-giver, Annie Potts as a bored receptionist, Ernie Hudson as an assistant who'll believe in spooks if there's a paycheck in it, and William Atherton as a Fed who tries to bust the ghostbusters.

The picture was directed by Ivan Reitman, who can sink to the most obvious kind of four-letter humor, then rebound with a clever touch or even a lovely one , as when Murray celebrates an upturn in his love life by spinning in ecstatic circles on a sunny Manhattan plaza. Although the project reportedly cost more than $30 million to complete, Reitman keeps the mood airy and light with only a few portentous lapses, mostly avoiding the temptation to grandiosity that spoiled such past disappointments as ''1941'' and ''The Blues Brothers.'' This is a silly movie, not delicate or subtle, but generally fun. I expect it will be with us for a very large part of the still-young summer season.

'Streets of Fire'

Walter Hill has made his mark as a slam-bang director of empty action pictures. His latest, ''Streets of Fire,'' is particularly slam-bang and empty, even by his high standard. You can see it as a tawdry melodrama or an exercise in pure cinema, but nothing in between. It's so stylized it's almost abstract.

The plot starts when a bad guy named Raven kidnaps a rock singer he has a crush on. Her old boyfriend and her mercenary manager (their names are Tom Cody and Billy Fish) go to the rescue, helped by a macho woman named McCoy. Near the beginning, Tom Cody burns down a section of the city. Near the end, he and Raven slug it out with sledgehammers. Yet the picture has a PG rating, so adept is director Hill at glossing over mayhem with a slick cinematic sheen.

The secret of watching ''Streets of Fire'' - subtitled ''A Rock & Roll Fable'' - is to see it as an elaborate joke. Once this is understood, you can find a goggle-eyed pleasure in its bizarre plot twists and rock-video rhythms. Some of the performances are also enjoyable in a rude sort of way, especially Willem Dafoe as the deftly demonic villain. It's a minor picture and sometimes a nasty one. But its energy is impressive.

'Coalfields'

Though its title suggests a dry documentary, ''Coalfields'' is an offbeat movie poem. Using a number of visual devices, including his own method of combining different images in one frame, filmmaker Bill Brand explores the industrial terrain of West Virginia with attention to political, economic, and personal matters while advancing his own film idiom at the same time.

The result is a dense and stimulating work, if a somewhat mysterious one. It will have its premiere tomorrow night at the Collective for Living Cinema in New York.

On one level, ''Coalfields'' deals with very objective subjects, including the problems of coal miners and the political difficulties of solving them. The filmmaker is more a visual artist than a social critic, though - he admits to being known as a ''formal purist'' - and over this footage he places a layer of complex, essentially abstract imagery that both interrupts and complements the basic material. This imagery is fragmented into crisp, angular shapes that suggest anything from lumps of coal to swarming birds. (Brand's father and grandfather were ornithologists, and his earlier film ''Chuck's Will's Widow'' has strong bird associations.)

Adding still more layers to ''Coalfields'' is a poem by Kimiko Hahn, ''sound composition'' by Earl Howard, and narration by a politically active miner. Brand tells me the film's objective content doesn't signal a move away from aesthetic purism and toward more socially oriented filmmaking, but it is rather a supplement to the formal concerns that still interest him most. Be that as it may, ''Coalfields'' is an inventive and visually provocative achievement.