Kenyan presidential candidate Raila Odinga speaks to supporters during an election rally in Mombasa December 22, 2007. Voters will go to the polls on December 27. REUTERS/Joseph Okanga (KENYA)

NAIROBI, KENYA —Citizens here may soon do something rarely done in Africa: vote out a president.

With the election set Thursday, challenger Raila Odinga has a narrow lead over President Mwai Kibaki, several opinion polls show.

That’s uncommon in sub-Saharan Africa, land of the Big Man, where leaders seldom are unseated — even if it means using their power to pull strings.

In Nigeria, the presidential vote this year was marred by allegations of widespread rigging. In Ethiopia, nearly 200 people were killed during postelection riots in 2005. Uganda’s president changed the constitution so he could run for a third term.

But Kenya is earning a reputation as an oasis of political stability in Africa, thanks to a succession of fair and stable elections, even when results defied the wishes of the government. In 2002 voters rejected then-President Daniel Arap Moi’s handpicked successor. Three years later they defeated a government-backed constitutional referendum. In both cases, there was little violence or backlash.

Now Kenyans say they are looking forward to exercising their democratic muscles again.

“These old men just don’t want to retire or accept the fact that they’re going home,” said Martin Kyalo, 32, an electrical engineer in Nairobi who plans to vote against the 76-year-old president. “We need to try someone else. We are crying out for change.”

Kibaki may yet secure a second term. Polls over the last several months show Odinga with a lead of only 4 percentage points. But the close race has been a reminder to politicians that voters in this East African country won’t be taken for granted.

Security guard John Nakitere, 30, said he planned to vote for Odinga because he is frustrated with inflation, stagnant salaries and unemployment. But Nakitere also has his eye on the 2012 election. “If Odinga doesn’t do any better, we’ll use the same knife to remove him from power in five years.”

There have been a few isolated instances of violence, chiefly involving local races, and a few allegations of vote buying or ballot tampering. One candidate for parliament was shot to death this month in a possible election-related assassination.

But most leaders, Western diplomats and voters expressed optimism that the vote would take place freely and peacefully.

“Do not hate your neighbor because he is supporting another party,” Kibaki urged Kenyans. “Do not assault him. Vote for the one you like. We shall be friends even after the elections.”

For Kenya, a third consecutive fair election would mark a significant step on its road to democratization. Just five years ago the nation lived under virtual dictatorship.

“We view Kenya as setting an example, not only for the East Africa region, but the continent as a whole,” said U.S. Ambassador Michael E. Ranneberger. “When you look at the democratic space in Kenya over the past five years, it’s remarkable.”

The upcoming ballot pits two of Kenya’s best-known politicians against each another. Both Kibaki and Odinga have served stints in the government and as opposition leaders. At times they’ve been political allies, other times rivals.

A third candidate, Stephen Kalonzo Musyoka, 53, is trailing in the polls, with support from 10% to 15% of respondents.

Kibaki is running on a campaign of unity and stability. The son of a goatherd, he joined the Moi government in the 1960s and served in various Cabinet posts. He later joined the opposition and ran unsuccessfully against Moi in 1998. He won the presidency in 2002, and his administration is credited with instituting free primary education, relaxing restrictions on free speech and news media, and revitalizing the economy, which grew 6% last year.

But his age and health have become a factor to many voters who believe that an accident weeks before his election in 2002 left him weakened and rumors that he has suffered several strokes.

His campaign promises to eliminate corruption fell flat after his administration was rocked by a contract scandal implicating top officials, including the vice president.

Odinga, 62, son of Kenya’s first vice president, was schooled in East Germany and named his first son Fidel, after Cuba’s Castro. He has since disavowed communism in favor of what he calls “capitalism with a human face.”

After a failed coup attempt in 1982, Odinga spent nearly a decade in prison, including a stint in Moi’s secret torture chamber in the basement of a Nairobi office tower.

After his release in the 1990s, Odinga surprised everyone by joining his jailer in a political alliance. He quit, however, when it became clear that Moi would not name Odinga as his successor.

In 2002, Odinga and Kibaki joined forces. Odinga agreed to set aside his own ambitions and supported Kibaki, who allegedly agreed to repay Odinga by backing his bid to become prime minister.

After the election, the partnership fell apart when, according to Odinga, Kibaki reneged on the agreement. Kibaki denied there was any such deal.

In his campaigning, Odinga has accused Kibaki of failing to stem corruption, which he said costs the government $75 million a year, and of pandering to rich fundraisers, some paying as much as $15,000 to attend posh dinners.

But Odinga also came under fire this fall when he started campaigning through slums in a $100,000 Hummer, which he said had been donated by supporters. And his appointment of American political strategist Dick Morris as an advisor backfired when Kenyans heard allegations about Morris’ relationship with a prostitute and tax problems.

In a hard-fought campaign that has galvanized the country for the last two months, seemingly no topic is off-limits — even the fact that Odinga is uncircumcised, in accordance with his tribe’s practices. Other tribes view circumcision as a rite of manhood, and one critic dismissed Odinga as a “boy.”

As is common throughout Africa, tribalism is playing a large role in the election.

The race in Kenya marks the culmination of a long-simmering rivalry, dating to independence in 1963, between two dominant political clans: the Kikuyu and the Luo.

Kikuyus, including Kibaki and the nation’s founder, Jomo Kenyatta, have been at the center of Kenyan politics since independence, enjoying the lion’s share of perks, including government jobs and land grants.

For Luos, the election and Odinga represent their chance to share in the spoils after watching several generations of leaders sidelined, marginalized or even slain.

“Politicization of ethnicity is a natural part of the political process in sub-Saharan Africa,” said Babafemi A. Badejo, a political analyst in Liberia who recently published a biography of Odinga. “Ethnicity is used to acquire power.”