TEN YEARS past Prime Time, Chevy Chase is still Chevy Chase (and, of course, we're not). The tanglefooted wiseacre is at the height of his comedy career with three movies opening this summer. First up is the mystery "Fletch," virtually a one-man show, a series of Chase scenes between co-starring cameos.

Fletch is a reporter in gumshoes, a Sam Spade with a deadline. But don't step over it. Or, bang, bang, you're history. I. M. Fletcher, alias Don Corleone, a.k.a. Igor Stravinsky, is also the funniest film sleuth since Inspector Clouseau. Like the dear inspector, he has a penchant for stumbling into trouble in a variety of preposterous disguises -- a Hare Krishna on roller skates or an L.A. Laker in an outsized Afro.

In fact, Fletch will do anything to get the story. "Ever do time, Doc?" he asks a no- nonsense proctologist in the middle of a prostate exam. Irreverent? Yes. Tasteless? You bet. But it's also a change of pace. Director Michael Ritchie refreshingly shows no reverence for film noir. And screenwriter Andrew Bergman, who co-wrote "Blazing Saddles," shows no mercy in what turns out to be a good mystery as well as comedy. Bergman's dual story lines converge in a quirky finish based on the Gregory Mcdonald novel but not totally faithful to it.

Fletch, disguised as a drifter, is investigating the drug scene when he happens on a better story. Aviation executive Alan Stanwyk (Tim Matheson), taken in by his disguise, asks Fletch to kill him, thereby saving the sick CEO from a lingering death and his lovely wife (Dana Wheeler-Nicholson) from losing the insurance money.

The suspicious reporter dons a series of disguises to learn the real truth. While many are outrageous, and in one case impenetrable, most rely on Band-Aids, fake teeth and sheer bravado. Dressed as a surgeon to get at Stanwyk's hospital records, Fletch is called to the aid of a pathologist during a particularly messy autopsy. And he slips on the linoleum floors in his surgical booties, like Gerald Ford on a muddy golf course.

Costar Richard Libertini, the demented dictator of "The In-Laws," is excellent in a straight role as Fletch's editor whose impatience puts the intrepid reporter in the slammer. Playing a Girl Friday, Geena Davis is delightful as always. M. Emmet Walsh is the aforementioned proctologist, and Kareem Abdul-Jabbar has a guest cameo.

Since "Fletch" author Mcdonald has already written sequels to his popular original, and since Chase is having so much fun on film, I'll bet, as we like to say in the news biz, there is More To Come.

FLETCH (PG) -- At area theaters.