The Oakland A's announced tonight they had fined Dave Kingman $3,500 for sending a small live rat to a female sportswriter and said he would be released if a ''similar incident'' occurs. Kingman had the rodent delivered in a pink box to Susan Fornoff of The Sacramento Bee during the first inning of Monday night's Oakland-Kansas City game.

The rat had a tag that said: ''My name is Sue.''

Asked earlier today if he would apologize, Kingman said, ''I've pulled practical jokes on other people and I didn't apologize to them.''

Fornoff said Monday night that Kingman had told her he did not believe women belong in the clubhouse and had harassed her at times since she began covering the team last season.

''The club has advised Kingman that if an incident of a similar nature occurs in the future, he will be released immediately without further compensation,'' the team's announcement said. In addition to the fine, the club apologized to Ms. Fornoff. In 1983, Kingman, then playing for the Mets, was reprimanded by the team for verbally abusing a female reporter.