A veteran NYPD officer pleaded guilty Monday to charges he helped run a gun-smuggling operation with fellow police officers that trafficked more than $1 million in illegal weapons and stolen goods. 

William Masso, of the 68th police precinct in Brooklyn, was arrested in October on charges of conspiring to sell M-16 rifles and guns in exchange for cash payments.

Twelve people were charged in the ring, including eight current and former NYPD officers. The FBI said the ring also sought to transport stolen goods like slot machines in exchange for payments.

Masso pleaded guilty Monday to four conspiracy counts.  He could face about six years in prison when he is sentenced on June 15.

The cases of the others arrested are still pending.

“An officer who betrays his badge betrays every honorable officer as well as every member of the public,” U.S. Attorney Preet Bharara said at the time of Masso’s arrest.

The FBI said Masso was caught on tape offering to transport stolen cigarettes and what he thought were stolen slot machines from Atlantic City.

Masso said he and his fellow officers should carry their badges and claim to be working off-duty for a client who purchased the goods at auction, prosecutors said.

Police Commissioner Ray Kelly said Masso’s actions were “a betrayal of the highest order of an officer’s oath.”

A spokesman for Bharara declined to comment.  Masso’s attorney Ron Fischetti also declined comment.