There's no denying it; the public service radio ad is cute and probably a help to Maryland consumers. A music from "The Sting" plays in the background, a hapless car owner who has asked his neighborhood mechanic to fix his car's brakes is handed a bill for a whopping $109.50.

"Why, you needed a tune-up," the mechanic [WORD ILLEGIBLE] replies when the customer questions the charge.

At this point a third voce tells the listener that under Maryland law you can't be charged or forced to pay for repairs you didn't ask for. "Take it from Maryland Attorney General Francis B. Burch," the voice urges.

Sure enough, on the air comes the voice of Francis B. Burch, one of more than a half dozen Democrats in Maryland running for governor. "Laws like this one can keep you from getting stung." Burch says authoritatively.

The problem with the public service ad, which is being run without charge across the state on radio and television, is that the ad first appeared Feb. 11, just as [WORD ILLEGIBLE] was gearing up for a major fund-raising drive for his candidacy.

The ads, [WORD ILLEGIBLE] effect, promote Burch's candidacy, charges Laurence Hulbert, executive director of the Maryland Republican Central Committee. Hulbert doesn't have anything against the ads themselves. It's Burch's role in them that he objects to.

"Though it seems the state is providing a valuable service, I tthink the taxpayers of Maryland ought to realize that they're paying for a political announcement for Francis Burch," he said. "Politically, I can see what Burch is doing. Incumbents try to take advantage of their office any way they can, but I wonder if a professional actor might be able to do a better job in this kind of thing than a candidate for office."

Burch dismisses such criticism, saying that state consumer protection law directs him to educate the public on such issues. "I'm not going to stop doing my job just because I may be a candidate," he said.

"This is something I've been doing for 10 years, and I don't intend to stop," he added in an interview. "If we don't do this kind of thing - educating the public - we might as well close up shop."

John Ruth, assistant attorney general for consumer affairs, said the taped ads were hand delivered to all major radio and television stations in the state in early February.

This was during the same period that Burch, a Baltimore Democrat, began inviting Key Democrats and wealthy political contributors to his home to talk about his still unofficial candidacy.

Earlene Moye, public service director of WTOP radio, said she didn't know Burch was a candidate for office when her station began running the ads Feb. 11.

Asked if that would have made a difference, she said, "It all depends. We'd have to take that up."

Ruth said the ads are patr of his division's continuing program of educating the public about consumer protection laws and are similar to efforts, the attorney general's office has been doing for a decade.

"The spot doesn't try to sell Bill Burch, or anyone else," he added. "It tells people what the law is."

Work on the ad began last July long before Burch had decided to run for office, and Burch wasn't involved until the final touches was made, Ruth said.

Ruth said the ads are-part of his di-Burch's voice be used. "To me, the message has more of a bang coming from the attorney general. When the attorney general says something is the law is has more credibility than when someone else says it."

The ads have been very successful, he said."One program manager called up to say he had trouble keeping one of his, disc jockeys from playing the ad every half hour. The guy has had trouble with car mechanics, and he's a maniac on the ad."

Ruth said he had considered the political implications of the ads. "It struck me that some time in the future someone might raise the equal time question," he said. "That's one reason his voice is really short on the ad."