By Patrick Worsnip

UNITED NATIONS, Oct 24 (Reuters) - Three days before key negotiations on Darfur, a U.N. envoy appealed on Wednesday to reluctant and disunited rebel groups to show up, saying they could still consult with each other after the talks open.

One of several obstacles to the talks between the Khartoum government and rebels from Darfur in western Sudan has been the rebels' inability to agree a common platform. The parties are set to meet on Saturday in the Libyan coastal town of Sirte.

Rebel leaders said on Tuesday a prominent Darfur faction chief and five smaller groups would not attend because African Union and U.N. mediators had not heeded requests for a delay to let them form a united position and agree a delegation.

But U.N. envoy Jan Eliasson, who will mediate in the talks along with AU envoy Salim Salim, said the "moment of truth" had arrived in the 4-1/2-year-old Darfur conflict and it was essential to get the talks going before momentum was lost.

Eliasson, talking to journalists at the United Nations by video link from the Eritrean capital Asmara, conceded that expectations might have to be lowered on talks U.N. Secretary-General Ban Ki-moon originally billed as "final".

Eliasson said invitations had only been sent out a week ago and he still did not know which among the more than a dozen rebel groups would come. "It's a moving target right now... I don't have the final list yet," he said.

International experts estimate 200,000 people have died and 2.5 million have been driven from their homes in the Darfur conflict, which began with a revolt against the Sudanese government, but Khartoum puts the death toll at 9,000.

Mediators say a cease-fire is their top priority at Sirte.

Trying to win over undecided groups, Eliasson said: "I want to very clearly make the point that the consultations that they are carrying on now ... will of course also continue in Sirte.

"We will allow plenty of time for the movements to have consultations among themselves, because the real negotiations will start only after we have the full preparations of the parties," he said.

"So there is a very grave responsibility resting upon the movements and the (Sudanese) government to come to the meeting," Eliasson added. Khartoum has said it will take part.

PRIORITY ISSUES

The U.N. envoy said, however, he now had "very little hope if any" that Sudan Liberation Movement founder Abdel Wahed Mohamed el-Nur, a rebel leader with a wide following in Darfur refugee camps, would come. El-Nur has demanded a string of concessions from Khartoum.

Eliasson also noted that Khalil Ibrahim, leader of the main branch of the Justice and Equality Movement, had asked for a month's delay. But he said he had assurances that Ibrahim would send high-level representatives to Sirte.

Apart from a cease-fire, Eliasson said other high priority issues would be compensation for villagers returning to their homes from camps, security and disarming militias.

Other issues, like power sharing and land ownership, would take longer. "But the main thing is that we stop the vicious circle, that we introduce the political element," he said.

He said fresh violence in Darfur, rising anger in camps, Sudanese government divisions and splits in rebel movements had all been "very negative" for the talks in recent weeks.

Such problems "may explain a different tone (in U.N. pronouncements) and perhaps the need to lower expectations somewhat," he said.

The Sirte talks have no fixed end date but diplomats say that rather than producing a settlement they may eventually adjourn and reconvene later, possibly at a different venue.

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