Tim Brant will be leaving his sports director's job at WJLA-TV-7 sometime next month, officials there said yesterday, to be replaced by Frank Herzog, now the No. 2 man to WDVM-TV-9's Glenn Brenner.

"It'll be two or three more weeks, but the sooner the better for me," said Brant, who for the last three months has, besides his Monday-Friday evening-news sportscasts for Channel 7, reported from the sidelines for ABC's USFL telecasts and handled segments for ABC's "Wide World of Sports." He is leaving WJLA for ABC, Brant says, with the promise of involvement in ABC's 1984 Olympics coverage.

Herzog's move could well heat up the continuing competition among the city's local sportscasters. Brant's sportscasts, up against George Michael's well-funded highlights machine at WRC-TV-4 and Channel 9's one-two punch of showman Brenner and veteran reporter-writer Herzog, have traditionally suffered from what's been perceived by many as a lack of commitment (i.e. money and air time) from WJLA.

David Pearce, news director for Channel 9, said "a piece of him (Herzog), I guess, has always wanted to be the No. 1 sports guy at a station in Washington. I can't offer it to him, of course. I'm delighted with Glenn. I'm also delighted with Frank. I'm happy for him and sorry he's going to be with the competition.

"I'm delighted," Herzog said. "It's something I've looked forward to and something I couldn't afford to pass up. I can still do the Redskins (radio play by play) and other outside work, and that was a big factor."