"Up and Coming" makes sermonettes and object lessons not only painless but poignant. The public TV series, funded by an HEW grant, is aimed at adolescents and deals with problems affecting minorities, but it avoids the goody-goodies that have infected such previous public TV forays into this field as last year's "Righteous Apples."

Thus it is proved that one righteous apple need not spoil a barrel. Producer Avon Kirkland has managed to shepherd "Up and Coming" through the obligatory gauntlet of PBS committees and PhD consultants into a realm very close to truth, especially for television.

On a recent episode of the series, produced at KQED in San Francisco, Lawrence Hilton-Jacobs (of "Welcome Back, Kotter") contributed a penetrating, moving portrayal of a young man who had resigned himself to shiftlessness; the program ended on a deftly sounded grace note of hope. One of the best things about the series is that it doesn't go pat on the problems it approaches.

Tonight's program -- at 8 on Channel 26 -- is the fifth in the series and deals with the pressures brought to bear on a black girl whose friendship with a white boy leads to rumors and ridicule among her peers at school. Rather than streamlining the dilemma into platitudinous mush, writers Theresita Conley and Bill Whitaker have the courage to grapple intelligently with its complexities.

Some in the cast of young people seem amateurish, but tolerably, maybe even endearingly, so. Others, like Renee Brown as the stalwart, no-jive Francine, and L. Wolfe Perry Jr. (once a Stanford U. basketball star) as Kevin, are impressively emphatic and sharp. Cindy Herron as Valerie, refusing to compromise on conviction or knuckle under to gossip, dominates the half hour with style and authority. This kid has her wits about her, and so does the show.

Wise counsel can be highly palatable when a story and characters are as dimensional and well thought-out as on "Up and Coming." The words-to-live-by include lyrics to the title tune: "The most you can ever do is the best you can." And the simple, invaluable remark of the kids' father, played by able veteran Robert DoQui: "You got to have pride in what you're doing, or why are you doing it?"

It's obvious that the people behind "Up and Coming" have pride in what they're doing, and in television, believe me, that is not to be sneezed at.