PREVIEW-Congo Republic's Sassou set for easy re-election

* Incumbent likely to win presidential election

* Opposition calls for a delay largely ignored

* Chance for president to improve nation's image

By Christian Tsoumou

BRAZZAVILLE, July 10 (Reuters) - Congo Republic's President Denis Sassou-Nguesso is all but guaranteed to be re-elected for another seven years in an election on Sunday that the opposition wants delayed but the government will push through.

Although expectations are low, analysts say a peaceful poll in a nation where elections have previously led to armed conflict could encourage investors to diversify the economy in Africa's No. 5 oil producer, which is mired by corruption allegations.

The run-up to the July 12 poll has been dominated by complaints by a plethora of opposition parties, who want the election delayed to iron out problems with the election commission, voter lists and the barring of some candidates.

But their wishes appear to have been largely ignored.