President-elect Mwai Kibaki promised Kenyans on Sunday an end to the government's authoritarian style and sweeping changes to battle corruption and staggering economic problems after his landslide victory over the party that ruled the East African nation for nearly four decades.

After Kibaki's opponent conceded defeat in the face of lop-sided 63 to 30 percent results, hundreds of the president-elect's supporters in trucks Sunday evening cruised down Nairobi's Moi Avenue, named for the outgoing president. Many waved leafy green branches -- an African symbol of a new beginning -- and chanting "Kibaki!"

Governing "is not a matter of promoting the ego of a president," the 71-year-old economist said to enthusiastic cheers from supporters who gathered at his colonial-era mansion. "A president should prove himself by things he's going to do which change the life or ordinary Kenyans."

He said he would propose legislation that would require top officials to declare their wealth and break with longtime traditions like hanging the presidential photo in shops and offices throughout the country.

Kibaki and his National Rainbow Coalition -- an alliance of opposition parties that won a majority in parliament in Friday's election-- intend to begin proving themselves soon: He will be sworn in Monday as Kenya's third president since independence from Britain in 1963.

However, there are no formal procedures for the mechanics of handing over power in Kenya, which has been run by one party, the Kenya Africa National Union, since independence. Outgoing President Daniel arap Moi has been in power since 1978.

Officials in Kibaki's alliance have been vague about what is actually involved in the transfer. A Western diplomat, speaking on condition of anonymity, said no formal arrangements for the transition have been made with Moi; he said a hasty inauguration could lead to some administrative chaos.

Moi had an autocratic style befitting the primary school teacher he once was, treating Kenyans as he may have treated his pupils -- he often told people KANU was their "mother and father." During the first 13 years of his rule, KANU was the only party allowed in the country, until multiparty politics were introduced in 1991. He also had a tendency to issue impromptu edicts that were rarely followed up, like declaring AIDS a national disaster but doing little the stem the spread of the disease.

Kibaki's promise of an economic revival -- and numerous other pledges, like free primary school education -- have raised hopes among ordinary Kenyans.

"It's like we've won our independence again," said George Owino, an unemployed 33-year-old from one of the sprawling slums that ring Nairobi, the largest city in eastern Africa.

In the United States, President Bush said he is looking forward to working with Kibaki. White House spokesman Scott McClellan said Bush also welcomed the fact that the elections were peaceful.

"The people of Kenya have chosen a new leader and all parties have acted responsibly in working to institutionalize democracy in Kenya," McClellan said.

Some say that Kenya's unbridled optimism is bound to give way -- "politicians will disappoint you, mark my words," Rev. Lucy Waruinge told parishioners at the All Saints Anglican Cathedral.

Moi was unable to run again because of constitutional limits. The KANU candidate he picked to try to succeed him, Uhuru Kenyatta, conceded defeat Sunday.

"KANU and I will respect him in his position in accordance with our constitution," said Kenyatta, the 41-year-old son of Kenya's first president, Jomo Kenyatta. He will be the leader of the official opposition after winning a seat in parliament.

Soon after, the Electoral Commission officially declared Kibaki the winner. With all but 14 of 210 constituencies reporting, Kibaki had won 63 percent of the vote, the commission said. Kenyatta had 30 percent.

The Institute for Education in Democracy, an independent monitoring group, put turnout at 56 percent of the country's 10.5 million registered voters.

Out of 192 seats confirmed so far from the 210-seat legislature, the Rainbow alliance captured 122 to KANU's 52. The remaining seats were divided among smaller parties.

Kibaki, who has been a leading opposition figure since multiparty politics were reintroduced in 1991, was Moi's vice president from 1978 to 1988. A London School of Economics graduate, Kibaki was also Kenya's longest-serving finance minister, holding the post from 1969 to 1982 -- a period of relative prosperity.

He placed second to Moi in 1997 elections and was third in 1992.

During his campaign, Kibaki promised to right the wrongs of four decades of KANU government, revive the country's ailing economy and fight rampant corruption -- a problem Western donors and international lending agencies have long said must be conquered before they can provide needed economic help.

If Kibaki's government does sincerely begin to fight corruption, that assistance will be forthcoming, the western diplomat said.

An economic revival in Kenya could be a boon to eastern Africa. The country's economy is the largest in a region where most countries -- Sudan, Somalia, Uganda and Ethiopia -- have been plagued by civil conflicts.

But in recent years the Kenyan economy has hit rock bottom, largely because of corruption and government mismanagement that has scared off foreign investors.

More than half of Kenya's 30 million people live on less than $1 a day, few have access to water or electricity and unemployment is rife.