The most intriguing work in the 75-minute compilation film that commemorates the Fifth Annual Student Awards Competition, scheduled for a 6:30 p.m. showing today at the Ameri-Film Institute Theater, is the winner in the documentary category, "The Sixth Week" by John Simeon Block of New York University.

Block's subject is a confessed compulsive gambler identified as Ralph U. who evidently falls off the wagon at the end of six wager-free weeks and is certainly upstaged by his long-suffering, disparaging, nasal wife Annette in a series of domestic exchanges perhaps unmatched for lower middle-class comic authenticity since Robert Kaylor's underrated, priceless "Derby."

Ralph and Annette scarcely qualify as an exemplary couple. Indeed, you're not sure how this marriage has survived or if it ought to survive. Husband and wife seem to have achieved some screwball balance of incorrigibility, with him habitually backsliding and repenting and her habitually taking him back in a spirit of sarcastic resignation.

Since Ralph and Annette appear to have spent at least 20 years perfecting this mutually dependent vaudeville act, it may be far too late to break in new partners or contemplate a new act. Their five children look well cared for and relatively impervious to the sniping recorded between dad and mom while Block was on the scene.

It's interesting to see how comfortable Ralph and Annette are with the rationalizations of pop psychology. Typically, she summarizes his gambling compulsion by observing that "he's just self-destructive... the screws are loose up here, you know; they flip out." On his part Ralph seems fond of self-assessments like the following: "I'm sick.... I'll never get cured; anything could trigger me off; an argument with my wife could trigger me off." Especially an argument with his wife, one gathers.The experts wouldn't approve, but in some dizzy way these two desperately need each other.

The other winners in this year's student film competition, co-sponsored by the Academy of Motion Picture Arts and Sciences, the Academy Foundation and the Bell System, were "Button, Button" by Burton Lee Harry of Arlington and the University of Bridgeport in the dramatic category, Matthew Patrick of Hampshire College for "Triptych" in the experimental category and David Bishop of USC for "Mother Goose," a mischievous three-minute animated film in the tradition of "Godzilla Meets Bambi."

Originated by the Motion Picture Academy, the student film competition draws entries from over 300 participating colleges and universities. The Bell System defrays most of the costs, including the staging of an annual awards presentation at the academy's theater in Los Angeles. The compilation film, which combines scenes from the awards ceremony with showings of the winning student films themselves, is offered free of charge to non-profit institutions through the College and Educational Relations office of the Bell System.