Ethnic and regional affiliations have long been central to Kenya's politics.  As Derek Kilner reports from Nairobi, general elections on December 27 are not expected to be different, with Kenyans voting in large part along tribal lines.

President Mwai Kibaki's support base lies with his Kikuyu tribe, the biggest in the country.  In largely-Kikuyu Central Province, he is expected to receive 90 percent of the vote.

His chief rival, Raila Odinga, belongs to the Luo tribe - Kenya's third largest, whose population is concentrated in Nyanza Province in Kenya's west, where Mr. Odinga is polling more than 80 percent.  His pick for vice president, Musalia Mudavadi has delivered strong support from the Luyha tribe, Kenya's second-largest.

Mr. Odinga argues that wealth, government positions and other resources have been concentrated among a Kikuyu elite under Kibaki.  This position has helped Odinga rally support from other ethnic groups that have also felt marginalized. 

He leads in every province with the exception of Central and Eastern, the strongholds of Kibaki and third-place Kalonzo Musyoka, respectively.

President Kibaki's inroads with other tribes, meanwhile, have been limited, beyond the Meru and Embu who have traditionally allied with the Kikuyu.  The third-place candidate Kalanzo Musyoka is polling at 43 percent in his Eastern province, but hovers around 10 percent nationally.

University of Nairobi Political Scientist Katumanga Musambayi cautions against simplistic assumptions about tribal affiliation.  He says Kenyans do not necessarily support candidates based on an inherent preference for people of a certain tribe, but rather for more practical reasons.

"The aspect of the tribe is blown out of proportion and I think it is a misunderstanding of the role it does play," he said.  "Ethnicity does not affect elections in terms of groups facing each other, but on the contrary it is about the instrumentalization of ethnicity.  It is not ethnicity for say, one group voting for the other actor because he comes from a certain ethnic group."

But he says voters are looking for the candidate who can deliver resources to their community, and this usually means the candidate who has courted support from tribal leaders.

"It is more about how a rational actor at a national level is able to construct assumptions or perceptions among the community that he has a better deal for them, given the fact that one of their sons or one of their daughters is part of his coalition," he added.  "So what you are beginning to see is that a large number, say in Western province is tilting towards Raila Odinga.  A large number of people in Central Province are tilting towards Mwai Kibaki."

Distribution of resources is also at the center of the debate over decentralization, arguably the main policy question in the election. 

Mr. Odinga has called for a more federal system of government, which he says would distribute wealth more equitably, but President Kibaki and his supporters say those proposals will exacerbate ethnic tensions. 

University of Nairobi sociologist Paul Mbatia says Kibaki supporters have focused on Mr. Odinga's use of the word "majimbo," a term for decentralization from the colonial period that has strong ethnic connotations.

"Those who oppose majimbo try to highlight the dangers of trying to divide Kenya along ethnic lines such that eventually we would be putting different ethnic communities in a competition or rivalry that may be destructive," he explained.

Clashes over land in the Rift Valley and Mt. Elgon regions of Kenya in recent months have highlighted the reality of the danger of ethnic violence in the country.  And Odinga appears to have responded to such concerns, backing away from the term "majimbo," though maintaining support for federalism.

There are indications that the importance of tribal affiliation in voting may be starting to wane, particularly among younger generations.  But for now, what Musambayi calls the "tectonic plates" of tribal voting blocks will remain at the center of Kenyan politics.