Dutch Marines backed by jet fighters today stormed a train where 51 hostages have been held for 20 days by South Moluccan gunmen. Other troops attacked the school where guerrillas were holding four teachers.

The attack began at dawn and heavy machine gun fire could be heard along with the boom of heavier weapons as the jets roared overhead.

The attack followed the breakdown of attempts by Moluccan mediators to negotiate a settlement with the gunmen who are seeking the independence of their island homeland from Indonesia and have demanded a getaway plane and the release of 21 Moluccan prisoners.

Associated Press reporter Arthur O. Sulzberger Jr., at the train site, saw four Starfighter Dutch insignia.

"The ground is trembling," the reporter said. "They're firing. A lot of firing. It's very concentrated.

"Everybody, reporters, photographers, police, army and are ducking down behind armored personnel carriers."

There was a bright red flash near the train shortly after the assault began and a few minutes later three large explosions appeared to come from within the train. However, the four-coach express remained intact.

After about 10 minutes the action appeared to have died down. Reporters at other vantage points said the train seemed undamaged and they did not think there was any shooting inside the carriages.

The attack began just before 5 a.m. (11 p.m. Friday EDT) with a crackle of small arms fire, followed by heavy gunfire.