David Bowie's pallor and passivity combine to give him somnambulistic glamor on the screen. As an object of contemplation, he's as riveting as Garbo, although he lacks the acting technique that would permit him to sustain her fascination.

Bowie was surprisingly effective as the melancholy extraterrestrial in "The Man Who Fell to Earth," currently in revival at the Key. He is less fortunate in a pretentious allegory called "Just a Gigolo," which was written off by its investors a couple of years ago and turned up in last weekend's presummer clearance openings, playing exclusively at the K-B Cerberus.

The setting is decadent Weimar Germany, depicted hypocritically with the tone shifting from the sinister to the mocking as director David Hemmings and screenwriter Joshua Sinclair make a spectacle of their astonishing hindsight, i.e., the big news that social decay and turmoil are encouraging the rise of Nazism. While avoiding many of the pitfalls that Ingmar Bergman insisted on jumping into during "The Serpent's Egg," Hemmings also enhances your respect for "Cabaret," still the definitive backward glance at the Weimar (1919-1933) period.

Hemmings seems to have aggravated his problems by reserving the role of the principal Nazi conspirator, a homosexual ex-officer named Capt. Kraft, for himself. At any rate, his performance gets a bit overipe in the direction of feline menace. Bowie sleepwalks elegantly through the surrounding hoopla, in the role of a symbolic lost soul, Paul Przygodski, the aimless scion of a Prussian military family. Returning from the war, Paul finds his father catatonic and his mother (Maria Schell) reduced to taking in boarders and working in a Turkish bath. A menial job leads Paul into the orbit of Capt. Kraft, who seems to be headquartered literally underground in a couple of sidetracked subway trains.

Paul appears to represent disillusioned, vulnerable postwar Germany, a prize up for grabs among contending predators. Paul himself has no discernible will, ambition or sexual drive, but possessing him seems to mean a lot to Kraft, to an adventuress played by Kim Novak and to an avid childhood sweetheart (Sydne Rome) who achieves fame as a movie star and fortune as the bride of aristocrat Curt Jurgens. Theoretically, having Paul also matters to Marlene Dietrich, cast as a procuress who recruits him to her stable of sleek young gigolos, but it's so painfully watching Dietrich try to speak or move that one loses the fictional thread. Like Mae West in "Sextette," her figure seems so mummified that you're too distressed by her condition to consider playing along with the make-believe.

The continuity is so wayward that the contest for Paul's fragil body and soul never generates any suspense or tension. It might have helped, of course, if the weak-willed protagonist had character flaws that decisively inclined him toward one patron or one form of dependency. The circumstances that lead to his eventual exploitation as a bogus Nazi martyr in the tradition of Horst Wessel are too arbitrary and expedient to earn the pat on the back for Devastating Irony that Hemmings and Sinclair award themselves.