One of Johnny Carson's recent guests was Lynn Redgrave, star of the newly revamped and partially recast version of NBC's "Teachers Only," a situation comedy returning tonight at 9:30 on Channel 4. Carson wished Redgrave well and said he hoped the show would succeed. And who could doubt his sincerity? "Teachers Only" is a product of Carson Productions.

America gets a well-deserved rest tonight from "The Winds of War," but there have to be a million better ways to spend the time than with "Teachers Only," a sleepy slice of pallid smarm if ever one there 'twas. This is the kind of comedy in which all the characters can be divided into two categories: the horny and the boring. While Redgrave does float with some charm above the throng, she unfortunately comes off like nothing more timely than a latter-Day Doris.

The plot of tonight's re-premiere has Redgrave, as Diana, spurning the advances of a supposedly desirable male (women in the audience go "Whooo!" when he nibbles her ear--thus setting back ERA another couple of years), then trying to deal with her feelings of jealousy when her dear pal Sam (Teresa Ganzel) goes out with the same guy a little later.

One of the teachers helpfully summarizes the plot this way: "Diana gets dumped by some creep who then hits on her best friend." That summary has as much wit in it as the entire program does.

Larry Rosen and Larry Tucker wrote and Charles S. Dubin directed this slow and shallow charade. Even the basic idea--a series about a school that relegates students to the background--lacks potential. These aren't the kind of people you want to spend a half hour with once a week. Ten minutes would be stretching it.