Undated (AP) _ Ten railroad cars carrying fuel oil and highly flammable butane derailed Tuesday in North Dakota, forcing up to 500 people to evacuate, and an Amtrak passenger train derailment in Pennsylvania was blamed on sabotage.

No injuries were reported in either accident.

Three of the tank cars containing butane tipped over near Wyndmere, N.D., but tests showed they were not leaking, said State Fire Marshal Robert Allan. There was no fire or explosion.

However, as much as 20,000 gallons of fuel oil leaked into nearby ditches from three fuel oil cars that overturned, Allan said at a news conference. There did not appear to be any threat to groundwater, he said.

Tom Tamlyn, a Wyndmere city councilman, said the evacuation would continue throughout the night as officials worked to remove the cars.

Most entrances into Wyndmere in southeastern North Dakota were barricaded and National Guard units were asked to help prevent the possibility of looting in the largely vacant town, Tamlyn said. School was cancelled.

A total tting an obstacle placed on track owned by a strike-bound railroad.

The Capitol Limited was en route from Washington, D.C., to Chicago via Pittsburgh. The two locomotives and 10 passenger cars remained upright on the tracks near the Youghiogheny River after the lead locomotive jumped the tracks.

''Preliminary reports indicate the derailment may have been caused by vandalism, a maintenance-of-way equipment rerailer having been placed on the track,'' said Amtrak spokesman Clifford Black. A rerailer is a metal device used to push work equipment onto the track, he said.

The tracks are owned by the Pittsburgh & Lake Erie Railroad, which is being struck by about 750 union employees who object to a proposed sale of the financially ailing railroad to Chicago West Pullman Transportation Corp.

P&LE spokesman Charles R. Craig said the accident ''was a direct result of sabotage.''

He said the rerailer ''was strategically placed on the tracks to cause a derailment.''

Craig said the FBI was asked to investigate and that inspectors from his railroad, CSX Transportation, Amtrak and the Federal Railroad Administration were at the accident site Tuesday.

William LaRue, spokesman for the Union Coordinating Committee, said Amtrak and P&LE were irresponsible in claiming vandalism caused the derailment.

''We don't know that,'' LaRue said.

Amtrak officials said Capitol Limited passengers were placed on four buses to continue their trip.

The derailment occurred on the same P&LE track where 16 cars of a CSX freight train, four of them containing hazardous chemicals, derailed Aug. 22. About 700 McKeesport residents were evacuated for 24 hours.

Sixteen cars of an 18-car Capitol Limited train carrying 234 passengers derailed in the Greenfield section of Pittsburgh on Aug. 15. None of the 234 passengers or 10 crew members aboard were injured.