* Politicians pass law on final day of parliament
* Elections could be delayed over logistical problems
* Opposition warns of unrest, wants foreign involvement
By Jonny Hogg and Bienvenu Bakumanya
KINSHASA, June 15 (Reuters) - Congo's parliament passed an electoral law on Wednesday, a crucial step toward organising Nov. 28 presidential and legislative elections, but opposition leaders have expressed concern over the poll's credibility.
The law, passed after weeks of wrangling, was little changed from the document that governed the last elections in 2006, lawmakers said.
The timetable for registering millions of voters is tight, and opposition parties want greater international involvement in monitoring preparations for the election.
President Joseph Kabila, who has reduced the contest to one round and is likely to face a divided opposition, is favoured to be re-elected. But the poll -- the second since the war ended in 2003 -- will take place amid insecurity and social tension.
The most pressing challenge is the registration of millions of voters spread across the vast Central African nation, roughly the size of Europe but desperately lacking basic infrastructure.
The latest figures from the election body show that 22 million people have been registered, leaving little time to reach the target of an estimated 31 million by the end of July.
"(Voter registration) may last longer than expected and the electoral authorities may be forced to prolong it, especially in Kinshasa," according to Thierry Vircoulon, a Central Africa analyst at the International Crisis Group think-tank.
"After the finalization of the voters' registration, there should be a checking of the voters' list to avoid duplication and this will take time too," he added.
FOREIGN INVOLVEMENT
Opposition leaders have complained that corrupt officials, broken equipment and a shortage of registration centres are damaging the credibility of the registration process and may delay the elections.
Kabila's current five-year term is ends on Dec. 6.
Remy Masamba, a top official in the UDPS, the party of leading opposition candidate Etienne Tshisekedi, said outsiders should step in as "caretakers" if there were delays.
"Any extension of (the government's) mandate should be accompanied by their removal from the electoral chessboard. That's why we're coming to need the international community to find a solution which guarantees the principles of fairness and justice," he told Reuters.
Foreign donors played a crucial role in helping Congo hold successful polls in 2006 and are still due to provide 40 percent of an estimated ${esc.dollar}700 million to fund this year's polls.
But Kabila has tried to limit foreign intervention in Congo's politics over the last five years, and diplomats will not have the same power to intervene to resolve disputes.
Thomas Luhaka, secretary general of the MLC, another leading opposition party, said delaying the vote would be dangerous as Kabila would have no mandate and talks would be needed with the opposition to stem unrest.
"The poverty of the population has reached such a point that the anger of people against the government could spread onto the streets. The security forces aren't equipped, trained or paid well enough to control a mass popular demonstration," he said.
Congo is trying to recover from decades of misrule and a brutal war which ended in 2003, leaving more than 5 million people dead and much of the country's infrastructure in ruins.
Despite the restoration of stability in some areas and increased foreign investment in sectors like mining, the IMF and the central Bank have warned that rising fuel and food prices are a major threat to the population, many of whom live in extreme poverty. (Editing by David Lewis and Tim Pearce)
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