The D.C. Police Department has been ripped off.

Sometime between Friday night and yesterday morning, two helicopter engines worth $12,000 each were stolen from a police warehouse at South Capitol and I streets SE.

The unusual theft was discovered when officers went to the warehouse for an engine to replace another that had burned out on one of the department's four helicopters.

They found the locks on two warehouse doors smashed and two of 18 helicopter replacement engines stored inside missing.

The 500-pound VO-435 Lycoming engines were encased in 3- by 4-foot steel cannisters that police estimated weigh almost a ton each by themselves, and officials last night were unable to explain how they were removed.

"Two or three people couldn't just pick them up and lift them out," said Sgt. Thomas Seddon, helicopter branch operations supervisor. He suggested that the thieves would probably have needed a heavy truck and a fork-lift.

Seddon said the warehouse, used primarily by the police fleet management division to store autos and auto parts, is surrounded by a fence, but is not guarded at night. Officals said the building is owned by the Exxon Corp., which allows the police department free use of it. The building is scheduled for demolition in the near future.

In fact, police said, the demolition company had already changed the locks on the warehouse over the weekend, and these apparently were the ones the thieves broke open to gain entry.

Not many people would have an immediate use for helicopter engines, Seddon said. "You can't set them in your back yard, and they're too big to go through the door of a house."

They could be used to power propeller-driven boats, as well as helicopters, Seddon said, but he was unable to suggest other possible uses for them.

Police officials said the engines were surplus military hardware and were reconditioned during and after the Vietnam War by Lycoming, the Pennsylvania manufacturer. "They're as good as new," said one helicopter branch member.

Officials said the helicopter branch, which is headquartered at National Airport, acquired a number of the engines four years ago to replace engines as they wear out in the department's fleet of Bell-47 machines.

Seddon said that since then the reserve engines had been stored without incident at the Southeast warehouse, along with other police equipment.