Support is growing for former Marine Ryan Jerome, who was busted trying to check his Indiana-registered handgun at the Empire State Building in September.

Jerome, 28, of West Bend, is threatened with a criminal record for gun possession and a possible mandatory minimum prison sentence of 3 1/2 years.

A letter-writing campaign launched by Jerome’s fellow Marines and urging the charges be dismissed — described in the New York Post — has snowballed via the website leatherneck.com thanks to the publicity, said organizer and Marine veteran Davis Bruce, a Boston-based lawyer.

“We’re just trying to get the case moved to the ‘dismiss’ pile,” said Bruce, who said he has received another 40 letters from Marines that he’ll be forwarding to Manhattan DA Cyrus Vance, Mayor Bloomberg, and Police Commissioner Raymond Kelly, who is himself a Vietnam Marine veteran.

A “Free Ryan Jerome” Facebook page is getting hundreds of hits and comments, and the story is being picked up by news outlets across the country, said Jerome’s lawyer, Mark Bederow.

“I’m asking the DA to dismiss the gun charges against this Marine and anyone else arrested solely for the crime of carrying a registered gun into the city, said City Councilman Dan Halloran, (R-Queens), one of several local pols who is taking to the airwaves and speaking out on Jerome’s behalf.

Jerome — a TOW gunner before his honorable discharge in 2005 — is “honored and grateful” for all the efforts, said his lawyer.

Jerome is a jeweler who had traveled to New York with $15,000 worth of gold he was taking to a Long Island refinery. Although he was busted under a weapons charge that carries a 3 1/2 year minimum sentence, prosecutors actually have great discretion in disposing of gun cases, and typically make distinctions between totally unregistered guns and those that are actually legal in the defendant’s home-state, like Jerome’s.

The Marines rallying to Jerome’s side are hoping that the charges can be dismissed outright or greatly reduced, as happened last week in the case of Tea Party activist Mark Meckler, who got a disorderly conduct plea deal after trying to check his California-registered Glock at LaGuardia Airport.

The city has seen a spate of publicized tourists-with-guns arrests in recent months. Charges remain pending against nurse Meredith Graves, who tried to check her Tennessee-registered .32-caliber pistol at the 9/11 memorial in December, and Fred Vankirk, caught with three Ohio-registered guns in his Midtown hotel room a week ago.

On Jan. 4, Stephen Grant got a misdemeanor plea deal for the Maryland-registered gun found in his Midtown hotel room this Spring. Jerome is due back in Manhattan Criminal Court March 20.

litaliano@me.com