Take a gushy adjective from one reviewer, throw in hyperbolic phrases from a few more, mix with a generous helping of superlatives, add three exclamation points, and you've got the hottest recipe in movie promotion today: the composite rave. The phenomenon takes single words and phrases from various film critics' reviews and combines them into one long, glowing blurb adding footnotes to explain the sources. Though Disney tried this cut-and-paste print-ad concept back in 1987 with Good Morning, Vietnam, the technique is gaining considerable ground today, especially at Universal, where Closet Land and The Hard Way offer the most recent examples of montage blurbs. (Neither Disney nor Universal will comment.) New York magazine movie critic David Denby, whose blurbs have appeared in other footnote ads, sees the technique as ''the latest wrinkle in stupidity'' by publicity-hungry studios. ''If you open the newspaper,'' he says, ''it looks like movies are a succession of masterpieces. Adjectives are becoming meaningless.''