United Nations officials vowed today to remain in East Timor to oversee an upcoming vote on independence, despite Tuesday's organized attack on one of its field offices by rock-throwing militiamen. But a separate attack later today on another isolated U.N. outpost raised the stakes in the escalating war of nerves between United Nations monitors and armed, anti-independence militiamen trying to disrupt the planned August referendum.

The latest incident occurred in the town of Viqueque, about 55 miles southeast of the capital, Dili, when about 15 armed militiamen stormed a U.N. compound and threatened staff members. Seven of the 14 U.N. diplomats were evacuated from the town, officials said.

The incident, just one day after the violence at a U.N. field office in Maliana, seemed to indicate the attacks were more orchestrated than spontaneous, and it suggested a new effort by militias to frighten or intimidate the world body into withdrawing before the vote. The militias, backed by the Indonesian army, have accused the U.N. of favoring supporters of independence for the troubled territory.

Meanwhile in Dili, U.N. officials said they were told Monday that a field office attack was imminent in Maliana, but Indonesian police, who are responsible for providing security for U.N. personnel in Timor, ignored the warnings. As a result, the diplomats said, the office and 12 staff members were left largely unprotected against the 100 or so attackers.

Eventually a riot squad appeared after a U.N. policeman escaped the compound and called for help. By then, a U.N. diplomat from South Africa and about a dozen Timorese were injured. About half of the U.N. staff , responsible for preparations for the August independence referendum, have now been pulled out of Maliana.

The accusation that Indonesian police failed to heed warnings of an attack was likely to escalate the war of words between U.N. officials and Indonesian government spokesmen, who continued today to insist that Tuesday's violence was merely a brawl between feuding Timorese factions.

Another sign that the Indonesian government has hardened its position on East Timor came when the Foreign Ministry announced it would bar Timorese Nobel laureate Jose Ramos-Horta from visiting his homeland ". . . because the majority of East Timorese people will reject his presence," said Information Minister Yunus Yosfiah.

The anti-independence militias in East Timor, with backing from the Indonesian armed forces, have been waging a campaign aimed at halting movement toward a vote favoring independence. The militias have accused the United Nations and foreign journalists of bias and have threatened to attack foreigners.

Special correspondent Atika Shubert in Dili contributed to this report.