A brazen car thief stole an NYPD highway patrol vehicle with a loaded shotgun inside this morning — and drove it all the way to La Guardia Airport — after a cop left it idling and unmanned while he got breakfast at a Bronx diner, authorities said.

The heist occurred at the corner of Cruger and Lydig avenues in Morris Park shortly before 8 a.m. when an officer grabbed a bite to eat at Lydig Coffee House, said sources.

The car thief sped away in the hot wheels, a marked Chevy Tahoe, and headed over the Whitestone Bridge, said sources.

Witnesses said the red-faced officer was only in the diner for two minutes when he ran out in a panic.

“All of a sudden I see a cop come out of the restaurant running. He was going crazy,” said Sammy Obaid, an employee at a deli across from the greasy spoon. “He was on the phone, making calls. He was freaked out.”

Obaid said a customer came out of the diner got in a car with the officer to try to chase down the suspect, but they returned empty-handed to the scene after a few minutes.

About a half-hour later, two rookie Port Authority officers found the heisted car at La Guardia Airport, parked at the lower level of the US Airways terminal. They arrested the suspect inside the main terminal at 8:30 a.m. while he was on an Avis Car Rental phone, according to sources.

When PA cops approached the suspect, he had handcuffs dangling from his waistband and was carrying a blue clipboard, police paperwork, a police identification kit that scans drivers’ licenses and a wad of $100 bills, sources said.

The suspect said, “Oh, you got me,” when cops approached. But then told them that he was an officer.

In a nearby bathroom, PA police also found a stashed luggage bag and a police utility bag.

Police took thee suspect to the 49th Precinct in the Bronx for questioning.

At mid-morning, a swarm of NYPD officers was inspecting the vehicle, which was still idling at the airport. A loaded shotgun in the vehicle was not taken and remained locked in the car’s rack.

Flights in and out of LaGuardia appeared to be unaffected.