* Communique to be approved at summit on Friday
* Preparations for referendums are behind schedule
* Analysts fear delay could spark renewed civil war
By Louis Charbonneau
UNITED NATIONS, Sept 24 (Reuters) - North and south Sudan will vow on Friday to ensure that a referendum on whether the south should secede takes place peacefully and on time, according to a draft communique obtained by Reuters.
The communique is expected to be approved at a summit on the sidelines of the U.N. General Assembly where U.S. President Barack Obama will join Sudanese Vice President Ali Osman Taha and Salva Kiir, the president of semi-autonomous South Sudan.
Preparations for the referendum, as well as another plebiscite on whether the disputed oil-rich region of Abyei will remain with the north under Khartoum or join the south, are behind schedule. Both are planned for Jan. 9, 2011.
"The CPA parties (north and south) expressed strong commitment to make all efforts to ensure peaceful, credible, timely, and free referenda that reflect the will of the Sudanese people of these areas," said the draft communique.
The CPA refers to the 2005 Comprehensive Peace Agreement that ended decades of civil war between the north and south.
"They further committed to overcome the remaining political and technical challenges and to ensure the referenda are held on 9 January 2011," the draft said.
Analysts fear any delay, or a messy outcome to the vote, could spark a return to civil war, with dire consequences for the surrounding region.
The draft statement also expressed "concern" at the continued violence in Sudan's western Darfur region, where the United Nations estimates as many as 300,000 people have died since 2003 when rebels rose up against Khartoum.
The Khartoum government's Darfur death toll is 10,000.
Sudan has said it hopes to begin registering voters for the referendum on southern secession next month, though U.N. officials say privately that they think registration is unlikely to start before November.
The point of Friday's summit -- and the presence of Obama -- is to send a strong signal to north and south Sudan that the world is committed to helping Sudan ensure the secession referendum happens on time, U.N. diplomats and officials say.
A successful southern referendum could bring a conclusion to one of Africa's most bitter conflicts, which has rumbled on since around the time of Sudan's independence in the 1950s.
A return to war would have a disastrous impact on Sudan, the nine countries that surround it and beyond, complicating existing conflicts and threatening areas of relative stability and growth such as Ethiopia, Uganda and Kenya.
Western powers, already deeply concerned about the spread of Islamist extremism in Somalia and the Sahara, have always been worried about security in northern Sudan, once a refuge for Osama Bin Laden and other militants.
Former U.S. President Jimmy Carter this year went as far as warning that a collapse in Sudan's peace process could spark a faith war between Sudan's Muslim north and the non-Muslim south, pulling in their religiously aligned neighbors. (Editing by Arshad Mohammed and Jerry Norton)
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