San Francisco -- California's two biggest outdoor advertising firms have agreed to post free anti-smoking billboards throughout the state to settle claims they ran cigarette ads too close to schools.

Eller Media Co. and Outdoor Systems Advertising, billboard companies headquartered in Phoenix, Ariz., agreed to donate 500 "billboard months'' of advertising space to carry anti-smoking messages targeted at young people.

Each company will carry free anti-smoking billboards provided by the state's Tobacco Control program on signs throughout California. A billboard month is a display of one sign in one location for one month.

"This is fantastic,'' said Michael Green, executive director of the Center for Environmental Health, a San Francisco-based advocacy group. "This is a perfect way to help protect the public from being addicted at a young age to a carcinogen.''

The group filed a civil lawsuit in March against the companies after a Chronicle story disclosed that tobacco billboards remained standing in San Francisco months after a state law banned them within 1,000 feet of a school or playground, a prohibited zone that included most real estate in the city. The suit charged that the companies flouted the state statute.

In May, the two firms volunteered to pull down all their tobacco advertisements in San Francisco, regardless of how far they might be from schools or playgrounds, and promised to be fully compliant with the law statewide by July 1.

"We're pleased to have this matter resolved,'' said George Broder, a spokesman for the Oakland office of Eller Media. He said the company does not admit to any wrongdoing. The state billboard restrictions took effect January 1.

Two-thirds of the billboards included in the settlement will be the large, "30-sheet'' signs typically seen from major highways. The agreement also includes smaller billboards and signs posted on bus shelters.

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