CHICAGO (AP) _ Playboy declared itself the winner Wednesday in a race with Penthouse to get nude photos of rock star Madonna to the newsstands and what is expected to be an eagerly waiting public.

The September issue of Playboy - with Madonna on the cover and an inside spread of 6-year-old black-and-white nude photos - was going on sale Wednesday in New York and Chicago, magazine officials said. It was to reach newsstands in other major cities Thursday.

Penthouse announced, meanwhile, that its September edition - with similar attractions - would be available in some major markets Thursday.

''We're always a step ahead,'' said spokeswoman Elizabeth Earhart Norris at Chicago-based Playboy Enterprises, Inc.

Playboy decided to move up the release date by a couple of weeks because of the ''overwhelming interest in the Madonna issue,'' Ms. Norris said.

She said Playboy's September issue was printed before Penthouse announced Sunday that photos of Madonna would appear in an unspecified future issue. Because the September Playboy already had been printed, the early release did not involve significant additional costs, Ms. Norris said.

Sy Presten, a spokesman for Penthouse publisher Bob Guccione, said the only change in that magazine's normal publishing procedures was getting its September issue out early.

Newsstand vendors were expecting brisk sales of both magazines.

''I've had some people ask me about it,'' said Jerry Calcagni, owner of Redig's Randolph Street Books in downtown Chicago. ''I expect it to sell out like the Penthouse pictures of Vanessa Williams did last year.''

''I want all the copies I can get,'' said Rick Graff, who operates Rick's Newstand on a busy downtown corner. ''I could have sold 10,000 of the Vanessa Williams' issue if I had them.''

Ms. Williams forfeited her 1984 Miss America crown after nude photos of her appeared in Penthouse.

''We expect both to sell out,'' said Paul Davidson, vice president and general manager of Charles Levy Circulating Co., which distributes Playboy and Penthouse to 2,600 Chicago-area outlets.

Meanwhile, plans to give Madonna her a key to her hometown have been scrapped in the wake of the Playboy-Penthouse battle.

''We'll give her a warm welcome,'' said Bay City, Mich., Mayor Timothy Sullivan. ''But the key represents the citizens of the community, and it would not be in good taste to give her the key, given certain circumstances.' '

And in New York, Madonna - who recently achieved rock stardom and also appeared in the movie, ''Desperately Seeking Susan'' - filed suit Wednesday in U.S. District Court seeking to stop production of a motion picture, also called ''Madonna.''

The suit, which seeks damages of $10 million, says the producers have tried erroneously to imply there is a connection between the singer and the movie.