Friendly-dumb rather than nasty-dumb, and therefore vaguely tolerable, "He's the Mayor," premiering at 9:30 tonight on Channel 7, is obviously not the show that is going to set ABC back on the road to success. A weak sitcom about the adventures of a young black mayor in a typical American town, the show seems to represent the end of an old era at ABC rather than the beginning of a new one.

In other words, when new ABC Entertainment President Brandon Stoddard said in Los Angeles the other day that television has to start treating its viewers with more "respect," he was not thinking of shows like "He's the Mayor."

Kevin Hooks, genial and likably sly in the part, plays the 25-year-old mayor, whom we meet two weeks into his first term. "Upset Victory" is how a newspaper headline, glimpsed in the opening credits, puts it. The comic foils include the mayor's insufferably wise old blue-collar father, played by Al Fann (sample wisdom: "You've got to be willing to fight for what you believe"); a jivey cliche' of a first cousin, also the mayor's chauffeur, played by Wesley Thompson; a sharp-tongued secretary, played by Mari Gorman; and a thick-witted WASP councilman named Nash, played by David Graf.

The neatest comic moments on the premiere are the exchanges involving terminally rumpled Pat Corley as the chief of police, who fixes withering stares that stay fixed (and don't wither). He plays very smartly off both Hooks and Thompson. Corley used to show up as a weather-beaten coroner on "Hill Street Blues" and, later, as the beleaguered team owner on "Bay City Blues." He brings dignity to a silly role on a silly program.

In the premiere's plot, the mayor has promised city workers a pay raise but can't deliver it because his father and a friend (Stanley Brock) buy a fishing boat, which doesn't make any sense, but then, this is not the kind of program that invites lingering over details. The studio audience, for its part, is in such a receptive mood that it probably would have gone gaga over a hectic game of mumbletypeg.

Hooks really holds his own and comes up a savvy survivor, no thanks to the simplistic script by coproducer Bob Peete nor the nervous direction of Oz Scott. While they thankfully rely little on racial jokes, the whole premise of the program, that a black mayor is some kind of bizarre new American novelty, seems dated, to be kind about it. There is a reference in the script, however, to Los Angeles Mayor Tom Bradley, who incidentally yesterday declared Jan. 9 "He's the Mayor" Day in L.A. A nice gesture, but it isn't very likely that the rest of the country will be joining in the celebration.