(adds Solana comment)

By Lamine Ghanmi

TRIPOLI, Oct 25 (Reuters) - Disarray in both government and rebel ranks makes quick progress unlikely in Darfur peace talks billed by the United Nations as a "moment of truth" to stop 4-1/2 years of violence in western Sudan.

The best that can be hoped at the gathering in Libya which begins on Saturday is agreement to meet again, this time with a wider, more inclusive array of parties to the conflict to end one of the world's worst humanitarian disasters, experts say.

"If I were the facilitators I would be seeking to build down expectations for this first round," said Larry Rossin, a former U.S. and U.N. diplomat who now represents the Save Darfur Coalition, an umbrella group.

The conference seeks to end a conflict that has sparked U.S. accusations -- dismissed by Sudan -- of genocide. Much of the killing, rape and looting has been blamed on a government-allied militia known as the Janjaweed.

Recently, however, rebels have been blamed for deadly attacks on African Union peacekeepers and aid workers. In some cases, experts say, the rebel command structure has broken down to the point that the groups represent no constituency and are nothing more than bandits.

Experts estimate 200,000 people have been killed and 2.5 million uprooted in violence since mostly non-Arabs took up arms in early 2003 accusing Khartoum of neglect. Khartoum puts the death toll at 9,000 and says the West exaggerates the conflict.

Many rebel leaders will not attend, including Abdel Wahed Mohamed el-Nur, founder of Sudan Liberation Army (SLA) rebel group who commands few troops but has wide popular support, in protest at what they call government-inspired violence.

Even those who will turn up "are not welded together into any form of coherent delegation with any form of position at this stage. A lot of Darfurians sense themselves going into something whose basis they are unsure of," Rossin said.

Mediators had hoped as many rebels as possible would attend and negotiate a comprehensive ceasefire. Since a peace deal signed by only one of three rebel negotiating factions last year, the insurgents have split into more than a dozen groups.

NORTH/SOUTH TENSIONS

On the government side, revived north/south tensions could complicate the U.N.-sponsored negotiations in Libyan leader Muammar Gaddafi's hometown of Sirte.

The former southern Sudanese rebels, the Sudan People's Liberation Movement (SPLM), withdrew this month from the national coalition government.

The SPLM has a 28 percent share of government but suspended its ministers, saying the dominant northern National Congress Party was stalling on a 2005 Comprehensive Peace Agreement (CPA) that ended Africa's longest civil war.

"The two issues are closely linked," said Sudan expert Alex de Waal. "On the Darfurian side there's no point in signing an agreement with a government that's about to collapse."

"And the reality is the CPA cannot proceed effectively while Darfur rages, because Darfur has the potential to spill into Kordofan and if it does then the whole country goes up in flames in one way or another," he said, referring to a central region.

Nur has said he would not attend the talks until a U.N. force was deployed to stem the Darfur violence, which has surged anew in recent weeks with civilians, African Union peacekeepers, militias and rebels caught up in clashes in southern Darfur.

Ahmed Abdel Shafie, another prominent rebel leader, and five other smaller factions announced at a meeting in Juba this week they would also not attend the talks, saying African Union (AU) and U.N. mediators had not heeded rebel requests for a delay to allow them to form a united position and agree on a delegation.

Added to Nur's refusal to attend, this would mean no rebels representing Darfur's largest tribe, the Fur, will be negotiating with Khartoum in Sirte.

Experts have said the May 2006 peace deal failed because international diplomats forced it on the Sudanese players despite the fact that it did not have widespread support among Darfuris. Within days of its much-heralded signing, violent protests were staged against it in Darfur camps.

De Waal said U.N. had "set a trap for itself" again by insisting the talks proceed despite the rebel demand in Juba for another month to organise themselves.

Proceeding without them meant the opportunity for peace was likely to be squandered, he said.

EU foreign policy chief Javier Solana said the talks were "the moment that all should live up to their responsibilities".

"As a first and indispensable step, the violence should stop. All parties should commit themselves unequivocally to a cessation of hostilities, and to participation in an effective ceasefire mechanism," he said in a statement in Brussels. (Additional reporting by William Maclean in Algiers, Ingrid Melander in Brussels)

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