JUST YOU AND ME, KID - AMC Carrolton, AMC Skyline, Aspen Hill, Inner Circle, Laurel Cinema, Springfield Mall and Tyson's Twin.

If gray power means anything, George Burns ought to be able to make as much a fool of himself at 83 as Brooke Shields does at 14 without unpleasant reflections being made as to his competence.

However, the phrase "old enough to know better" does spring to mind to distinguish his failure from hers in their pediatric-geriatric comedy, "Just You and Me, Kid." A successful 77-year career as a comedian might warn one against a comedy in which every other joke is one of those face-savers that nightclub comedians need for covering a silence that was supposed to be filled by laughter.

There's something terribly sad about this failure, not because of the actor's age but because the important question of age-prejudice is raised in the story. Good points are made about such perils as depression, fixed incomes and the vulnerability to accusations of senility, but they are made by a fool of a character pitifully trying to pass himself off as cute. Burl Ives and Ray Bolger are among those who play, as Burns does, retired vaudevillians; but they, too, are made to look silly.

Now, Shields is dreadful, too, and it doesn't reflect on the competence of all early-teen film stars. Although, come to think of it . . . CAPTION: Picture, BURNS AND SHIELDS STAR IN "JUST YOU AND ME, KID."