In most of Maryland, the already bitter contest between Baltimore Mayor William Donald Schaefer and Attorney General Stephen H. Sachs for the Democratic gubernatorial nomination has barely registered with an electorate that sees little reason to get excited 237 days before the primary.

But on Main Street in Laurel, the battle has already been joined.

The first volley was fired Jan. 6, when Laurel Mayor Robert J. DiPietro opened headquarters for a group known as Marylanders for Schaefer and strung a large political banner with the group's name on it outside the office on Main Street.

Marylanders for Schaefer is an independent committee whose purpose is to nudge Schaefer to make his unofficial gubernatorial candidacy official. It operates with the blessing of Schaefer, who raised $1 million at an October fund-raiser but has not yet declared he will run.

Volley number two came when John Chamberlain, a 77-year-old retired engineer and Sachs partisan, took it upon himself to research the Laurel city sign ordinance. He discovered that political signs may be no larger than 32 square feet and may not be posted earlier than 30 days before an election.

"I took a squint at the sign," Chamberlain said. "It's about four feet by fifteen feet, almost twice the legal size. And it's certainly more than 30 days before the election."

Believing that "the mayor has to enforce his own ordinances," Chamberlain wrote a letter to the Laurel Leader newspaper, with a copy to DiPietro, pointing out the breach.

DiPietro said the sign was only one of several temporary advertising banners that were placed at the new Patuxent Place retail complex to call attention to the commercial development and its tenants. Nonetheless, DiPietro acknowledged that the banner "was in violation of the ordinance," and took it down yesterday.

But the 33-year-old DiPietro, who has been Laurel's mayor for eight years, said the sign affair "has turned out very nicely" because it will make Schaefer believers out of the owners of every business that doesn't conform to the sign ordinance.

DiPietro says he going to insist that all signs in Laurel that violate the ordinance be replaced. He's already ordered a city survey of signs and promises that every offender will be told his signs are coming down, courtesy of the Sachs campaign.