NAIROBI - Two heavyweights of Kenya's post-independence politics square off in a presidential vote on Thursday that has overshadowed Christmas and seen the opposition hold a small lead in opinion polls during the campaign.

The closeness of the vote has raised fears fraud and intimidation may be used to try to swing results in a nation that has enjoyed relative stability and become east Africa's economic power-house since the end of British rule in 1963.

All except one of the public surveys since September have put opposition candidate Raila Odinga - a 62-year-old businessman and former political prisoner - a few points ahead of President Mwai Kibaki, who won in 2002.

Just one recent poll, by Gallup, put Kibaki a point ahead, showing that all is still to play for in an election entertaining Kenyans' minds far more than the festive season.

Around the capital Nairobi and other major towns, sparse Christmas decorations were swamped by party colours and vast posters of the main candidates.

"This is not likely to be a season of good cheer due to the very human clash of wills between contenders for political power," wrote the Daily Nation in a Christmas Day editorial.

"As a result, society is more polarized than ever before."

After a rough campaign, including several deaths and riots, many locals worry about more trouble on the day.

"The temptation to rig is always there, but it is heightened by the fact the election is very competitive," Koki Muli, co-chair of a domestic observers' group, told Reuters.

Her group, the Kenya Election Domestic Observation Forum, is sending between 17,000 and 20,000 locals to most constituencies across Kenya. International missions, from the African Union to the European Union, also abound, though smaller in number.

They will be assessing the state of democracy in Kenya which experienced a rarity in African politics five years ago - the largely peaceful transition of power from a "Big Man" ruler.

Analysts say a possible "nightmare scenario" is a narrow government victory, aided by rigging.

"Then you are going to see the Raila camp go absolutely ballistic, because they've led polls," a Western diplomat said. He predicted such an outcome would produce rioting in Nairobi and Odinga's western homeland Nyanza.

ECONOMIC CREDENTIALS

Kibaki, 76, elected a legislator for every term since independence, hopes economic record of average 5 percent annual growth will win him a second term, before then retiring to his highland farm.

He has the support of his economically powerful Kikuyu tribe, the largest of Kenya's 40 or so ethnic groups, and has tempered his aloof image with skilful grassroots campaigning - in Mandela-like flowery shirts - in recent weeks.

Odinga has the ardent backing of his western Luo community, but has also garnered support from other ethnic groups who think the Kikuyus have had it too good under Kibaki.

Dubbed the "kingmaker" for helping Kibaki's 2002 win, before splitting with him over a referendum in 2005, Odinga belongs to one of Kenya's elite political dynasties. His father is left-leaning independence hero Jaramogi Oginga Odinga.

Both men are pledging broadly similar policies of increased economic growth along free-market lines and an extension of free education to include secondary schools.

Their pledges to outlaw corruption, however, have fallen on sceptical ears given that Kibaki's government has failed to tackle graft, while Odinga's team includes some people implicated by media and campaigners in scandals.

"The elite will always look after themselves," said Geoffrey Odindo, a street-cleaner on 3,500 shillings (28 pounds) a month.

Some 14 million of Kenya's 36 million people are eligible to vote from 6 a.m. (3:00 a.m. British time) to 6 p.m. (3:00 p.m. British time) on Thursday.

Official results are expected to start coming in from Friday morning, though media surveys will give a picture overnight.