Indonesia is planning a major military action against the nationalist guerrillas on the Southeast Asian island territory of East Timor, according to eyewitness reports from Timorese refugees arriving here in the Portugese capital.

The refugees say the military operation is being launched as a "final onslaught" against the insurgents following the breakdown of a fragile cease-fire negotiated in March.

Since the renewal of hostilities in mid-August, the refugees claim the Indonesians have increased the number of troops stationed on the island to about 20,000.

In addition, they also claim that 200 to 300 Timorese women and children were massacred in the southern coastal region of Viqueque last month.

[Officials at the Indonesian Embassy in Washington denied any planned military action against the guerrillas. Information officer Ngurah Gedhe said he did not know how many troops were stationed on the island, but he said he did not know of any recent buildup. He also denied reports of civilian deaths.]

[U.S. officials in Washington said they had no evidence to support the refugees' claim of a massacre, but they did confirm that Indonesia appeared to be planning military action. They said the reported estimates of 20,000 troops appeared to be high. Before the cease-fire, there were an estimated 6,000 to 8,000 troops on the island, the officials said.]

According to refugee reports, the alleged massacre was carried out in retaliation for the killing of 15 Indonesian off-duty troopers after fighting broke out at a dance on Aug. 9, before the breakdown of the cease-fire.

The refugees say they are fleeing because they fear renewed food shortages in January. Islanders were forced to take part in military building projects and could not tend crops, they said.

East Timor, a former Portuguese colony, was stricken by widespread starvation in the wake of its annexation by neighboring Indonesia in 1976 when relief agencies estimated that more than 200,000 subsequently died, victims of famine, disease and the hostilities.

The refugees asked not to be identified because they feared reprisals against their families remaining on the island.

Describing the buildup of the new offensive, one refugee who arrived here Sept. 9 said that since mid-August waves of paratroopers had been arriving daily by sea and air, accompanied by tanks, helicopters and planes. He said civilian trucks had been commandeered to move armaments throughout the island and that helicopters regularly brought wounded Indonesians and Timorese to the hospital in Dili, the capital.

Refugees also reported that Indonesian occupation forces have imposed a dusk-to-dawn curfew, evacuated civilian Indonesians from Dili and airlifted alleged guerrilla sympathizers imprisoned on offshore islands to the more distant island of Bali.

[In Washington, Indonesian Embassy and U.S. officials said they had no evidence to support these claims.]