Once, not too long ago, the art crowd had little use for commercial fashion photography. These fashion layouts, so they sniffed, with their puffs of taffeta and fey posturings, could never equal fine art pictures of more serious subjects -- like rocks and trees.

Now, of course, such thinking has been laid to rest. Not only are fashion photographs traded in the art marketplace for big money, but museums and galleries have embraced many an image of the well-turned heel and back-lit coiffure. Call it glamor. Call it nonsense. Call it a just reward for a group of artists who could find work only in the slick pages of dream magazines.

Horst P. Horst, for one. The darling of the fast set, the Conde' Nast photographer since 1932 who made his assumed stutter of a name with a corset advertisement, Horst said the other day that he never imagined his work would be part of an exhibition in a gallery. But part three of the "Master of Fashion Photography" series at the International Center of Photography (1150 Fifth Ave. at 94th Street) is lovingly devoted to 40 years of the 78-year-old photographer's theatrical charades.

Like a glimpse into a Jean Harlow movie, the Horst retrospective is pure fantasy. "Have fashion; will travel" reads the caption under a 1955 advertisement he produced for the Cadillac Eldorado Seville, and we believe it. Designer Pauline Trige re reclines languidly in her bra and slip. Paloma Picasso hides behind a dark shadow and a pair of forbidding Karl Lagerfeld shoulders. A young Lucino Visconti looks vulnerably out at the world.

By the end of the exhibition, however, elegantly installed under his flip moniker in the ICP's handsome Federal period town house, "Horst" seems more an exercise in supercilious nostalgia than a serious art show. Nevertheless, the fashion world turned out in full force to celebrate one of the nicest men to ever stand behind a camera. (Through Nov. 4.)