Louis Lowell McGuinn was a regular at military galas around town, posing with a gleaming chest full of medals that symbolized a life of valor.

But another vet noticed in December that McGuinn seemed to be wearing the Purple Heart, the Silver Star and the Distinguished Service Cross incorrectly - and a 40-year lie started to unravel, prosecutors said.

Yesterday, Manhattan federal prosecutors used a brand new law to charge McGuinn with posing as a war hero - making the Flushing, Queens, man one of the first in the New York region to face prosecution under the Stolen Valor Act.

The law, which took effect in January, makes it a felony to falsely claim to have received an award authorized for members of the U.S. armed forces.

He faces a year in jail.

McGuinn, also known as Lowell Craig McGuinn, served in Vietnam and was a private when he was discharged from the Army in 1968.

But over the years he bumped himself up to lieutenant colonel to help him win lucrative security consulting contracts, prosecutors say.

The feds have photos of McGuinn, 62, at military events at the Pierre Hotel and the Merchant Marine Academy in Kings Point, L.I.

In December, McGuinn leased space at the Soldiers, Sailors, Airmen and Marines Club in midtown, where the club's executive director noticed McGuinn "wore decorations on his uniform in the incorrect manner and, when asked, could not produce any documentation verifying his service or medals," according to a criminal complaint filed by FBI Special Agent Jason Randazzo.

In December, Randazzo said McGuinn told a New York City police officer he was a lieutenant colonel working with the Department of Homeland Security. He told executives at an underwater marine security company that he served with the Special Forces, the feds say.

He was released on $5,000 bond after a brief court hearing.