The biggest score of all at the Super Bowl might be made by Mayor Bloomberg.

In an unprecedented move, the mayor and his national coalition against illegal guns plan to air a 30-second ad during the big game, which draws some of the highest TV ratings of the year and traditionally serves as a platform for memorable and very expensive commercials.

Bloomberg disclosed today that he and Boston Mayor Tom Menino — who serves as both co-chair of the mayor’s coalition and host mayor of the rival New England Patriots — have already filmed the ad that’s going to be screened in selected regional markets on Sunday.

One of those markets will be Washington, D.C.

“A New York-Boston Super Bowl is a perfect opportunity for the mayors to talk about fixing the nation’s backround check system that allow criminals and dangerous people to buy guns illegally,” said Bloomberg spokesman Marc LaVorgna.

Bloomberg has been frustrated by Congress’ refusal to impose stricter regulations on sales at gun shows, even to the point where he’s authorized undercover sting operations in states across the nation to demonstrate how easy it is to circumvent federal weapons regulations.

Aides said the ad is still being edited and wouldn’t be finished for another day or two.

They provided a single picture from the shoot, which showed Bloomberg wearing a replica Giants tee shirt over his dress shirt with French cuffs, seated next to Menino in Patriots garb. Both were seated on a couch in front of a table with hats of their respective teams.

“It was very funny,” the mayor said of the ad, without providing further details. “You should take a look at it.”

Aides offered one hint, saying viewers should expect a play on the rivalry between Boston and New York.

National Super Bowl ads are fetching a record $3.5 million for 30-second spots.

The mayor’s ad is expected to cost hundreds of dollars, with the tab billed to Mayors Against Illegal Guns, which Bloomberg helps fund.

The mayor is traveling to Indianapolis to watch the Giants-Patriots showdown.

Asked if he had any advice for the hometown team, he responded, “Yes, win.”

“It’ll be a lot nicer trip back if you win,” he added.