* Congo Senate approves reforms reducing polls to one round
* Changes seen benefitting incumbent Kabila's re-election
(Adds analyst quote)
By Jonny Hogg
KINSHASA, Jan 13 (Reuters) - Congo's Senate approved proposed constitutional changes on Thursday reducing this year's presidential election to one round in a move likely to boost incumbent President Joseph Kabila's chances of winning.
Kabila has cited the crisis that erupted after Ivory Coast's two-round vote as justification for avoiding a run-off -- an argument rejected by opponents who threaten street protests against the move.
He says the vast central African country cannot afford two rounds of voting like in 2006, when donors paid hundreds of millions of dollars for elections that saw Kabila beat former rebel leader Jean-Pierre Bemba in a tense run-off after years of cvil war in which at least five million people were killed.
The upper house voted overwhelmingly for the reforms, which were adopted by the National Assembly on Tuesday and must now be approved with a 60 percent majority in a joint sitting of the two houses.
Information Minister Lambert Mende told Reuters the vote on the reforms, which also include rules for the powers of the president, would be held on Friday, the final day of the current parliamentary session.
Francois Mwamba, secretary general of the MLC, the biggest opposition party, said it would not take part in the debate in the joint session but would lobby against the reforms.
"We are going to carry on talking to the international community, so that they don't fall into this trap," he said.
The government estimates each round of voting will cost about ${esc.dollar}350 million and donors are seen less likely to stump up the cash for polls than for the first post-war election.
If approved on Friday, the new rules will mean that whoever gets the highest score in a sole round of voting will become president even without an absolute majority. Under a two-round system the top two must battle it out in a run-off.
While some of Kabila's opponents might have thrown their weight behind whoever of them made it into the run-off, it is unclear they would do the same in a single-round vote.
KABILA-MOBUTU ALLIANCE
Analysts say the move underscores Kabila's lack of confidence over his chances and could point to a turbulent run-up to the elections.
"This is an attempt at electoral fraud by Joseph Kabila," said Georges Nzongola Ntalaja, professor of African Studies at the University of North Carolina in the United States.
Ntalaja said it was not surprising the move had been passed so swiftly as Kabila, from the east of the country, had maintained his alliance with politicians from the west, including the family of former dictator Mobuto Sese Seko.
"The government has the ability to impose its will through a parliament that is basically rubber-stamped," he said.
Congo's 2006 election renewed investor confidence in the former Belgian colony after decades of dictatorship and conflict.
Riding high commodity prices and the relative stability, major firms returned to tap into copper and cobalt reserves and search for possible oil fields.
But Kabila has struggled to make good on many promises on development and pacifying the east, where rebel and lawless army units roam. His government has been accused of corruption and the business environment is still one of the world's trickiest.
Relations with United Nations peacekeepers, who helped provide logistics for the 2006 poll, have since soured and the world body's mandate in the country has been diluted to reduce the political clout it enjoyed during post-war years. (Writing by David Lewis; Editing by Angus MacSwan)
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