(Adds wrangling over oath of allegiance)

By Bryson Hull and Barry Moody

NAIROBI, Jan 15 (Reuters) - Kenya's parliament elected a speaker from the opposition on Tuesday, heralding serious legislative problems for President Mwai Kibaki after his disputed re-election last month unleashed a wave of bloodshed.

After three rounds of voting, Kenneth Marende, the candidate of the Orange Democratic Movement (ODM), achieved the required simple majority in parliament's first session since more than 600 people were killed in post-election violence. Marende won 105 votes against 101 for the government candidate, outgoing Speaker Francis ole Kaparo. The close ballot raised the prospect of deadlock in parliament and difficulties for Kibaki in passing essential bills.

In the 222-seat parliament, the ODM has the highest number, 99, after many of Kibaki's former ministers and allies lost their seats in the Dec. 27 election.

Reflecting the opposition's bitterness over what they see as a stolen victory, ODM members questioned why they should swear allegiance to Kibaki and not their leader Raila Odinga.

"In the eyes of the people of Kenya, Raila Amolo Odinga is president of Kenya," ODM's James Orengoh told the house.

"Do I swear allegiance to Honourable Raila Odinga or do I swear allegiance to Honourable Mwai Kibaki?" he said.

Although the new speaker overruled the complaints, the house was briefly disrupted when an ODM legislator swore allegiance to "President Odinga" and was ordered to retake the oath.

Kibaki's Party of National Unity (PNU) won only 43 seats but is trying to garner support from political allies to prevent obstruction by the ODM.

In a new blow to prospects for ending the damaging crisis, former U.N. Secretary-General Kofi Annan, due in Nairobi on Tuesday to head mediation efforts, delayed his mission for several days because of flu, his office said.

Foreign powers, like most Kenyans, are increasingly impatient with Kibaki and Odinga's failure to negotiate an end to the turmoil.

Thirteen donor countries, the European Union and the United Nations threatened in a statement to withdraw direct assistance to the government if its commitment to "good governance, democracy, the rule of law and human rights weakens".

Despite demands by Kenyans for urgent action, opposition and government legislators argued for more than an hour before deciding the poll for a new speaker should be secret.

"We went through (national) elections with a secret ballot, and you stole the vote," said senior ODM member William Ruto.

Justice Minister Martha Karua retorted: "Some people with the title 'Honourable' in this House are planning murder and instituting murder."

Roads were closed and riot police ringed the building as Kibaki and Odinga entered parliament at the same time, without looking at each other. It was the first time they had been in the same room since the December poll.

PROTESTS PLANNED

The parliament sitting began a new period of high tension after a lull in the crisis, with the ODM planning to defy a ban and stage three days of demonstrations from Wednesday.

Until he fell ill, Annan was due in Nairobi to head a group of "Eminent Africans" trying to mediate between Kibaki and Odinga.

"On advice of doctors he has postponed his mission to Nairobi for a few days," Annan's office said in a statement.

Graca Machel, wife of Nelson Mandela, and former Tanzanian President Benjamin Mkapa were due to join Annan.

Turmoil since the presidential and parliamentary elections has dismayed foreign donors, jeopardised Kenya's democratic credentials and hurt one of Africa's brightest economies.

Western powers, and Kenya's east African neighbours, have complained of irregularities in the presidential vote count.

Foreign diplomats want Kibaki, 76, and Odinga, 63 -- a one-time member of his cabinet and former political prisoner -- to meet and agree on a power-sharing arrangement or new vote. (Additional reporting by Duncan Miriri, Bryson Hull, Katie Nguyen, Nicolo Gnecchi in Nairobi; and Laura MacInnis and Stephanie Nebehay in Geneva; Editing by Alison Williams)

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