Cameron Stewart – The size of the planned UN observer force to East Timor next month may need to be increased because of unstable security in the territory, senior officials say.

UN planners will hold meetings in New York later this week to discuss the size and composition of the world body's presence in East Timor, which is expected to include up to 100 Australians.

The UN observer group for East Timor was expected to number between 400 and 650.

But senior UN officials said yesterday the number of monitors was likely to be higher than originally thought because of the poor security environment in the former Portuguese colony.

"If there is a security problem, as there appears to be, then [the UN] will be looking at putting in more people," one senior UN official told The Australian.

The UN personnel will not act as peacekeepers and Indonesia has said its troops will be responsible for security during the autonomy ballot.

However, the UN maintains that a large presence will help stabilise the security situation as well as maximising the safety of its personnel.

The UN special envoy for East Timor, Jamsheed Marker, said at the weekend that the presence in East Timor was likely to be "fairly massive".

The UN is preparing to send a group of non-military observers, possibly including civilian police, to East Timor to monitor a ballot on autonomy for the territory, which is expected to be held in August.

But officials said the final decisions about the size and composition of the UN presence in the province could not be made until it was known how the autonomy ballot would be conducted.

Indonesia has not yet disclosed how it intends to hold the ballot, which is described as a "consultation".

Jakarta does not want a full-scale referendum, while the former colonial power, Portugal, wants a fully democratic vote. Indonesia has promised that it will grant East Timor independence if, as expected, voters reject the UN-brokered autonomy package.

If Indonesia opts for a "mobile" ballot, where UN officials travel to individual villages to collect votes and bring them back to their central headquarters, then the number of personnel required would be less than if Indonesia adopts a one-man-one-vote fixed ballot located in every village.

Indonesia is expected to disclose the method of voting and the related security arrangements for the ballot on or before May 5, when Indonesia and Portugal will sign the autonomy package in New York.

Speaking ahead of yesterday's summit between Prime Minister John Howard and Indonesia's President B.J. Habibie, the Foreign Minister, Alexander Downer, said any UN presence in East Timor would need to be a large one.

"My own view is that it will be necessary to have hundreds of [UN] people to help with the consultation [election] process," he said.

"After all, you are talking about a possibility in the vicinity of 200 different polling stations. You've got 800,000 people in East Timor."