LIVINGSTON, MONT., NOV. 1 -- Hours after a strike began, three locomotives were set loose, careened along 13 miles of mountain tracks and plunged into a canyon, injuring a hobo, in what a railroad official called "a malicious act of sabotage."

Union leaders denied today that any of their members sent the crewless locomotives -- two of them new -- at speeds up to 100 mph along the tracks and into the canyon near Livingston in southwestern Montana at 2:30 a.m. Saturday.

About 150 United Transportation Union workers staged a strike Friday night to protest the sale of Burlington Northern tracks to the newly formed Montana Rail Link. Within two hours, picketers were removed under a restraining order obtained by the railroad.

Gary Widle, vice president of operations for Montana Rail Link, which assumed control of the tracks at 12:01 a.m. Saturday, said, "Somebody with knowledge of what they were doing got on a train at Livingston . . . pushed the throttle into full operating position, and nullified any features that would stop the train and apparently jumped off the engine."

He said damage was estimated at $3 million.

A hobo, Allan Eadie, was riding in the third locomotive. He was in stable condition with fractured ribs, a spokesman for Bozeman Deaconess Hospital said.

Howard Kallio, spokesman for Burlington Northern in Seattle, said, "I would call it a malicious act of sabotage. I think it's reasonable to suspect it was probably a rail worker."

John Post, head of the UTU local in Livingston, denied his members were involved.