NAIROBI, Kenya - A millionaire opposition leader who cast himself as a champion of the poor appeared poised to unseat Kenya's president, preliminary official results of the election and media tallies yesterday showed.

The race pitted President Mwai Kibaki against a former ally, Raila Odinga, and marked the first time an incumbent had faced a credible challenge in Kenya's four decades of independence from Britain.

The race focused largely on corruption, with both candidates vowing to end the graft and tribal favoritism that have tainted politics here for years.

A string of Kibaki's allies in parliament were also being unseated in the vote.

Kenyans clustered around radios and televisions as results trickled in. By yesterday evening, the electoral commission had announced preliminary results in only 68 of Kenya's 210 constituencies. They showed Odinga with a slim lead of 1,665,714 to Kibaki's 1,169,631. Media tallies said to be based on actual results showed Odinga with a more commanding lead.

Still, the slow pace of official returns raised fears of rigging.

Feeling confident of a win, Odinga's Orange Democratic Movement party said the government was deliberately delaying results because it was losing. Police appealed for calm as tempers flared.

A party official, Joseph Nyagah, said: "We'd like the ECK [Electoral Commission of Kenya] to announce the results in order to ensure that the political temperature does not go up."

Constance Newman, head of a U.S. observer group, said the official process was cumbersome, likening it to "molasses in winter." The European Union observer team said there was no immediate evidence of rigging.

Kibaki, 76, has been credited with helping boost this East African nation's economy, with a growth rate that is among the highest in Africa and a booming tourism industry. But his campaign against graft has largely been seen as a failure, and the country still struggles with tribalism and poverty.

Odinga, 62, a flamboyant former political prisoner, promised change and help for the poor. His main constituency is Kibera, one of Africa's largest slums, which is home to at least 700,000. But he has been accused of failing to do enough to help his constituents during 15 years as a lawmaker.