"One on One," now at area theaters, is a wobbly attempt at junior division "Rocky." Robby Benson, who played the juvenile leads in "Jeremy" and "Ode to Billy Joe," collaborated with his father, Jerry Segal, on this poorly rationalized, wish-fulfilling starring vehicle about a small-town prep basketball flash who is overwhelmed by the culture shock and ego bruises awaiting him at large university with a high-pressure athletic program.

The premise is fairly promising, and the movie has fitfully appealing interludes when the filmmakers are in a mood to treat the subject matter and protagonist humorously. Benson seems to perceive himself as a romantic hearthrob and sentimental darling, but he displays more talent as a comic stooge. His best scene is a slapstick manic outburst, reminiscent of early Jerry Lewis, when he is on uppers and gets carried away with enthusiam at basketball practice.

The movie sustains a certain comic verve and sense of proportion as long as it's content to view the Benson character, called Henry Steele, as the ignorant babe in the woods he essentially is and to take potshots at the subterfuges and hypocrisies of big-time intercollegiate sports. Whenever the mood shifts toward True Romance or pathos, the movie begins to disintegrate. The process of disintegration is built into Benson's self-righteously sentimental conception of Henry, the kid underdog, who is permitted to jerk one set of emotions when he appears to be falling and suffering, as other set when he's miraculously sent in to win the Big Game, and still another when he ostentatiously rejects the sports stardom we were conditioned to believe he valued.

Benson tries to have his cake and eat it, precisely the indiscretion avoided by Sylvester Stallone as Rocky, whose modesty made his fairy tale success more appealing. Benson also seems prone to vastly overrate his sex appeal. Here again he might have taken a useful cue from Stallone, who really has a potent sexual presence but probably enhanced it among both men and women by matching Rocky with a modest, ordinary girl like Talta Shire's Adrian.

Some people have the common touch. Other people merely flatter themselves that they have it while groping around for it. At this juncture Benson is still an amateurish groper. He looks hilariously overmatched opposite actresses as saucy as Annette O'Toole, Gail Strickland and Melanie Griffith. The idea that O'Toole, cast as a serious, older student hired to tutor the unbookish Henry, would rapidly find her disdain and pity turning into love is presumptuous in the extreme. It would make more sense if Henry simply imagined that this girl couldn't resist his charms, which are restricted to a kind of Little Engine That Could determination.

The movie might have derived more fun from the idea of Henry being seduced by the Strickland character, supposedly a secretary in the athletic department who can't keep her hands off the recruits. Both O'Toole and Griffith, who does a quick turn as a teenage hooker-extortionist, created striking impressions in Michael Ritchie's "Smile" two years ago. The premise of "One on One" might have been up Ritchie's alley, and there's every reason to belive that director Lamont Johnson, whose credits include "The Last American Hero," would have shaped the material in funnier, less mawkish wasys if he'd been involved from the start.

The best sustained performance in the movie is contributed by G. D. Spradlin as Henry's stern, ruthless college coach, a role that suggests a poison-pen caricature of John Wooden. Johnson himself appears as a jock-supporting alumnus. The most expendable elements in the show are the ludicrous songs by Charles Fox and Paul Williams which accompany transitional or time-killing sequences. One number, "Wagons, Ho?" is so terrible that it's almost classic.

Just as "Rocky" suggested the influence of several old movies that shaped Stallone's tastes and calculations. "One on One" is an index to Robby Benson's favorite films. In at least two instances he goes too far cribbing the scene from "The Hustler" in which Paul Newman tried to explain his love of pool-playing to Piper Laurie and envisioning Henry as the equivalent of Montgomery Clift's Prewitt in "From Here to Eternity" standing up under The Treatment as administered by coach Spradin. Really, Benson is going to have to learn how to moderate his fantasies if he expects us to keep a straight face.