JUBA Sudan, Aug 24 (Reuters) - South Sudan plans to bring home 1.5 million displaced southerners from the north in time to vote in an independence referendum in January, according to government documents.

The south is widely expected to choose to split from the north in the poll after a 2005 peace accord ended a two-decade long civil war and gave southerners the right to determine their own future by plebiscite.

The war drove 4 million people from their homes and the Ministry for Humanitarian Affairs and Disaster Management is targeting 1.5 million southerners in the north they say want to vote at home under a plan dubbed "Come Home to Choose".

"(The southern government) has taken up the challenge to organise the repatriation program for internally displaced persons wherever they may be in the northern states," according to ministry documents seen on Tuesday.

Half the proposed 60 million pound ($25.4 million) price tag is allocated for transport by truck, train, bus and boats traveling up the Nile. The other half is earmarked to cover logistics such as en route feeding and security.

Official voter numbers are not known for the referendum that will decide the future of Africa's largest country. Southerners living outside the semi-autonomous region will be able to vote once they prove their southern origins.

But some southern officials fear displaced voters in camps in the north are at risk of having their votes manipulated -- either by coercion or corruption -- and say they are very keen to install referendum voters in the south before polling day.

Aid agencies, however, are concerned about the impact of returnees on the humanitarian effort in the south.

In one of the poorest corners of the world, tribal conflict and bad harvests have to led to widespread hunger and internal displacement. The United Nations say it has already fed some 4 million southerners in 2010, almost half the region's population.

Plans for the referendum have long been delayed by squabbling between the north and south parties who signed the 2005 accord and voter registration has yet to begin.

The south's ruling party says the plebiscite must take place no later than Jan. 9, 2011.

(Editing by Opheera McDoom and Angus MacSwan)