Amtrak's 11:30 a.m. Metroliner from New York to Washington rammed a huge piece of track maintenance equipment in Edison, N.J., yesterday and the locomotive burst into flames. Seventy-three of the 200 people on board were injured, but none of the injuries was reported to be serious.

Amtrak spokesman Joseph Vranich said three people working on the track maintenance machine jumped clear just before the impact. The engineer applied emergency brakes to slow the five-car Metroliner.

The injured passengers were taken to three Edison area hospitals, where officials reported mostly cuts and bruises. There were some reports of back ailments, and all the passengers were "shaken," in the words of one hospital official.

"Glass was flying everywhere and people were flying down the hallway," 7-year-old Eric Massey, of Providence, R.I. told United Press International. "There was a fire and seats were broken. I was crying because my neck hurt."

The crash occured 38 minutes after the train left New York's Penn Station.

The train was somehow assigned to a track on which the huge "Track tamper" was working. This wheeled device, which levels rails and switches by adjusting the ballast under them, wights 32 tons and is 65 feet long.

The cause of the accident was being investigated by the National Transportation Safety Board and Amtrak. "We're interviewing crew members of both the train and tamper, plus the people in the switching tower," Vranich said.

Vranich said it had not been determined how fast the train was going when it struck the tamper. However, the tamper was pushed 300 feet and ended up crushed into the nose of the locomotive. The fire was confined to the locomotive, Vranich said, and was quickly extinguished by local firemen.

The accident closed all four tracks on the Northeast Corridor for about two hours, when two of the tracks were reopened. By early evening, most Amtrak service was back to normal, although speed restrictions through the crash area were causing delays of 15 to 20 minutes.

Uninjured passengers were taken by bus to Trenton, where they were placed on another train to Washington, Vranich said. CAPTION: Picture, Giant wheeled track tamper is rubble after being shoved 300 feet along the rail by passenger train in background. UPI