Former L.A. Law star HARRY HAMLIN got his first big acting break because of his willingness to drop his pants in public!

He was also a hippie with a long history of drug use, got kicked out of college, had an obsession with Playboy models and infuriated Ronald Reagan with his on-campus antics while in school.

Those are just a few of the titillating revelations in 59-year-old Harry’s new tell-all, Full Frontal Nudity – and The ENQUIRER has an exclusive sneak peek.

Harry, a native of Pasadena, Calif., evolved into a hippie wearing bell bottoms, long hair and mutton-chop sideburns who smoked pot and took LSD while a student at the University of California at Berkeley, he writes in the book.

After renting a cheap room at a fraternity house on campus, he was elected president of the Delta Kappa Epsilon fraternity.

Harry sparked the ire of then-California governor Ronald Reagan when he rented rooms in the fraternity to anyone who needed a place to live, including women. At the time, that was seen as highly inappropriate. Reagan called the campus a "haven for communist sympathizers, protesters and sex deviants," and wanted the young women thrown out along with an apology from Harry!

Harry refused and was expelled from school. He transferred to Yale University in Connecticut.

He returned to the Bay area after graduating and joined ACT – the American Conservatory Theatre – where he discovered his lifelong ambition was to become the "greatest actor in the history of the world," he writes.

His big break had little to do with his ability to act, though.

He made his mark in the acting community when he had to drop his pants and stand naked in front of the director for the lead role in the play Equus in 1976, he reveals.

"They needed an actor who wasn’t well-endowed and not afraid to drop his pants onstage in front of several thousand people eight times a week," says a publishing source.

"Harry got the gig and his first major acting success."

Harry also reveals that his parents gave him a five-year subscription to Playboy magazine when he was only 11, and that he became obsessed with Swiss actress Ursula Andress.

Later on, when he was 27, he met Ursula on the set of Clash of the Titans. They had an affair, and she gave birth to his son Dimitri in 1980!

"Those early years of Playboy nudes made an indelible mark on Harry," and he turned into an insatiable ladies’ man," continued the source.

His third wife, actress Lisa Rinna, posed for the bunny mag a year after their 1997 wedding, and again in 2009.

Along with the book, Harry and Lisa will debut their new reality show, Harry Loves Lisa, on TV Land in October.

Evidently their new TV show will be fully clothed.