No one could accuse Dan Aykroyd of waiting around for the perfect script to come along. "Doctor Detroit," now at area theaters, is as feeble a vehicle as any but the meanest mean spirit would ever wish on him, but it does allow Aykroyd to hop and romp through a variety of shticks--though probably fewer than he handled on a single week's installment of the original "Saturday Night Live."

Audiences may well wish he'd tossed in a few of those bits for old time's sake--a Tom Snyder, a Richard Nixon or a swinging Festrunk brother--and for the sake of the picture, which could use about a thousand more comic ideas than it has. In the farce, which never finds a tone for itself, Aykroyd plays a fussy college lit professor named Clifford Skridlow who, through pitifully contrived circumstances, becomes pimpo uno of a Chicago prostitution ring, metamorphosing at the drop of a pinkie ring into a garishly dressed, claw-handed alter ego called Doctor Detroit.

Aykroyd plays Skridlow as a sort of macho priss and the doctor with a grimace and a limp; the picture seems a curious cross between Don Quixote and Jerry Lewis as "The Nutty Professor." Near the end of the film, the limp is incorporated into a funny dance routine in a sequence that features James Brown and his ensemble; for a moment, the better parts of "The Blues Brothers" are recalled. But director Michael Pressman, who shows no aptitude for comedy up to this point, also shows no inclination to stay with a good thing, and so Aykroyd's crowd-pleasing dance is cut short. Pressman casts a real thud; he poops the party even when it makes a much-belated stab at getting frisky.

According to the plot, patched together by screenwriters Carl Gottlieb, Robert Boris and Bruce Jay Friedman, the schmo-ish Skridlow is recruited, through generous applications of mind-altering substances, by another pimp played by Howard Hesseman, his Hefty-bag face at full sleazy sag, because the pimp is in trouble with Mom, a Bru nnhilde of a madam whose other claim to fame is that she had successful colon transplant surgery.

Skridlow, transformed into Detroit, gets to play the avenger on behalf of the stable of four happy whores he inherited (one of them Donna Dixon, the lady of the high visual impact from TV's now-extinct "Bosom Buddies") and, later on, for all the good, pure and decent Chicago low-lifes Mom has wronged.

This premise is not so much supplemented by as dropped periodically for Skridlow's misadventures at the college, where his father is chancellor. A large corporation is about to save the impoverished school with a generous endowment for the Harold Robbins chair in literature (let's try to suppress our belly laughs) and Skridlow's frequent clandestine trips to the wild side threaten this plan, though half-heartedly at best, and often absent-mindedly as well.

In addition to the Skridlow and Detroit characters, Aykroyd briefly assumes the white suit, string tie and gravelly bluster of a southern lawyer, when the black prostitute in his charge is arrested for soliciting and sent before a bigoted judge named Robert E. Lee Davis-Jackson. Aykroyd makes the most of these ruses, and it's hard to judge his performance without considering the miserable excuse for material, but "Doctor Detroit" suggests strongly he is not capable of carrying a movie by himself (he'll be teamed next month in "Trading Places," a comedy with Eddie Murphy that sounds fairly promising).

There is some tangential support--from the ineffable Devo, which sings the title tune; from T.K. Carter, who surmounts the street-wise stereotype in his role as the pimp's chauffeur, and from a young actress named Fran Drescher, very slyly funny as prostitute Karen Blittstein, who takes over a catered dinner in classy bossy fashion and looks like she'd be just right for the lead role in "The Ann Miller Story." Unfortunately, she's all but misplaced until late in the picture.

These are fleeting inspirations, however, and when the picture falls back at fade-out time on the old "American Graffiti" character update routine, you know that the correct prescription for "Doctor Detroit" is, "Movie, heal thyself." DOCTOR DETROIT

Directed by Michael Pressman; screenplay by Carl Gottlieb, Robert Boris and Bruce Jay Friedman; story by Bruce Jay Friedman; director of photography, King Baggot; edited by Christopher Greenbury; music by Lalo Schifrin; executive producer, Bernie Brillstein. Produced by Robert K. Weiss for Universal Pictures. Rated R; 89 minutes.THE CASE Clifford SkridlowDan Aykroyd Smooth WalkerHoward Hesseman Arthur SkridlowGeorge Furth Monica McNeilDonna Dixon however, and when the picture falls back at fade-out time on the old "American Graffiti" character update routine, you know that the correct prescription for "Doctor Detroit" is, "Movie, heal thyself." DOCTOR DETROIT

Directed by Michael Pressman; screenplay by Carl Gottlieb, Robert Boris and Bruce Jay Friedman; story by Bruce Jay Friedman; director of photography, King Baggot; edited by Christopher Greenbury; music by Lalo Schifrin; executive producer, Bernie Brillstein. Produced by Robert K. Weiss for Universal Pictures. Rated R; 89 minutes. Clifford Skridlow . . . Dan Aykroyd Smooth Walker . . . Howard Hesseman Arthur Skridlow . . . George Furth Monica McNeil . . . Donna Dixon