NEW YORK (AP) _ An engine caught fire on a USAir jetliner just before departure for Boston, forcing passengers of the northeast shuttle to evacuate by chute and closing La Guardia Airport for about 90 minutes this morning.

None of the 44 passengers or seven crew members aboard the Boeing 727 was injured in the 6:45 a.m. mishap, said Paul Laude, a spokesman for the Federal Aviation Administration.

The plane was on the runway, ready to take off, when the blaze was spotted, said Paula Porcello, an FAA spokeswoman.

The passengers were evacuated and taken by bus back to the terminal, she said. After firefighters used foam to extinguish the blaze, one La Guardia runway was reopened at 8:10 a.m., the second at 8:22.

Officer Richard Boroski of the Port Authority police said the fire was in engine No. 1 of the three-engine jet. The cause of the fire was not immediately known.

An investigator from the National Transportation Safety Board was at the scene, Porcello said.

While Laude of the FAA said ''we consider this a minor incident,'' the engine fire came at an inopportune time for USAir. It recently took over the lucrative New York-Boston and New York-Washington routes from Trump Shuttle and is battling the competing Delta Shuttle for business.

Last month, a USAir jetliner taking off in a snowstorm crashed at La Guardia, killing 27 people.

USAir spokesman Stuart Benzal said the jet involved in today's incident was one from the former Trump Shuttle fleet. Although the FAA identified the flight number as 1170, he said that was the old Trump number and the correct flight number was USAir's 2902.

He did not confirm there was a fire, saying only that a passenger said heard a popping sound from the left side of the plane. But the FAA said airport tower personnel did see a fire.