NYC- A drug thug and his “Sopranos” actor sidekick who killed an off-duty cop were dumbfellas who drank themselves into a stupor at a topless joint before breaking into a Bronx apartment looking for Valium – unaware that the pad had been empty for months since the owner’s death, sources said yesterday.

The incredibly stupid – and ultimately deadly – saga was botched from the start: One member of the idiot duo, Steven Armento, was too fat to wiggle into the apartment window that he had broken, the sources said.

That left his skinnier pal, Lillo Brancato Jr. – who starred in the Robert De Niro flick “A Bronx Tale” and had a recurring role in HBO’s “The Sopranos” – to finish the dirty deed, squeezing through the window.

The stupid pair’s tale began after Armento, 48, a former Genovese associate, and Brancato, 29, spent Friday night and early Saturday boozing it up at the Crazy Horse, a Bronx strip club, the sources said. The club shares the same name as one featured in “The Sopranos.”

At about 4 a.m., the Yonkers men wanted some Valium, so they decided to rob the basement apartment of the deceased owner, Kenneth Scovotti, 63, where one or both of the men had once scored the tranquilizer, the sources said.

Brancato drove Armento to Scovotti’s home at 3119 Arnow Place in Pelham Bay. Armento then broke a window and tried to squeeze inside, but was too portly, the sources said.

So the actor, who has battled drug problems for years, allegedly climbed into the pad.

But he didn’t find any drugs.

That’s because apartment had already been completely cleaned out as part of proceedings by the Bronx Surrogate Court after Scovotti, who owned the building, died in July. His 1985 Oldsmobile was still parked across the street.

The pair of would-be burglars were walking away when they were confronted by Officer Daniel Enchautegui, 28, who lived next door. Armento pulled out his father’s old .357-magnum revolver and fired two shots, striking the officer in the spleen, authorities said.

Enchautegui fired back and hit Armento several times, including once in the penis. Brancato was hit twice in the chest. Both were in stable condition yesterday.

In a statement, De Niro said, “This is deeply disturbing news, a tragedy beyond comprehension. I join others in extending my deepest sympathy to Officer Enchautegui’s family.”

The account of the gun battle came as a clearer picture of the suspects emerged.

The young actor battled drug abuse so severe that relatives and friends staged an intervention three weeks ago, a neighbor said.

As in an episode of “The Sopranos” in which Christopher’s family confronts him about his addiction, the meeting at Brancato’s ex-girlfriend’s house went badly, neighbor Paula Azurieda said. In the midst of the meeting – attended by the actor’s brother – Brancato angrily ran into the street, she said.

Brancato’s mother, Domenica, yesterday defended him.

“He’s the best son a mother could have,” she sobbed.

Brancato’s manager, Garianno Lorenzo, said they had a massive blow-up over the actor’s drug use earlier this year.

“He kept telling me, ‘I can handle it,’ ” Lorenzo said. “I told him, ‘You can’t handle it.’ ”

Actor friend Patrick Cooley said the situation is shocking because Brancato lionized cops.

“They all recognized him,” Cooley said of Brancato. “He’d stop and pose for pictures, talk with the guys for a half-hour. He really felt the cops had done so much for New York.”

Brancato had been dating Armento’s daughter, Stefanie.

According to authorities, Steven Armento had committed burglaries as a low-level Genovese associate 20 years ago but had become such a junkie that the family cut him loose.