(adds Kibaki speech, updates death toll)

By Andrew Cawthorne

NAIROBI, Feb 4 (Reuters) - Kenya's president and first lady have disagreed in public over who is to blame for two fire disasters killing at least 148 people.

Their unprecedented spat has added to public dismay over the way authorities have reacted to a supermarket fire that killed 26 people and a petrol truck blaze with 122 fatalities.

During a week of national mourning for the east African nation's worst accident toll of recent times, First Lady Lucy Kibaki raised the political stakes when she lambasted one of her husband's ministers during a visit to victims.

The volatile Lucy Kibaki, who has in the past been accused of slapping a journalist and a politician, was angry at Security Minister George Saitoti's comments that poor Kenyans contributed to the oil disaster by scrabbling for fuel in the road.

"How can dead people be taught a lesson?" she said, visiting a hospital on Monday. "If it was a woman in the ministry of internal security, she would have stopped these accidents."

Abandoning his traditional low public profile at moments of national passion, President Mwai Kibaki stood by Saitoti in a speech outside his Nairobi office.

"I wish to assure my Minister for Security, Honourable George Saitoti, that I have full confidence in him," Kibaki, 77 said in comments published by local media on Wednesday.

RULERS TO BLAME?

Kenyan authorities have faced a torrent of criticism for poor safety standards and a slow response to the accidents.

Some survivors have said fire-escapes in the Nairobi supermarket were locked, while some witnesses of the truck blaze near Molo town accused police of taking bribes to allow people to start scooping up oil in the road before it caught fire.

The disasters have compounded a mood of national gloom in Kenya, where new graft scandals have come to light in the maize and oil sectors, and the economy has taken a dive due to the global crisis and the impact of last year's election violence.

East Africa's biggest economy is also facing a food shortage, with 10 million people -- or more than a quarter of the population -- suffering from hunger.

Trying to chart a way forward, Kibaki opened a three-day policy conference titled "The Kenya We Want". Many, however, are sceptical their leaders are the ones to take them forward.

"The problems we face were caused by the ruling class," said Morris Odhiambo, of the National Civil Society Congress.

"The current leadership, characterised by oligarchic claims to power and privilege, patronage and corruption, cannot deliver on the transformation Kenyans desire," added Odhiambo, who was organising an alternative conference in Nairobi.

Kibaki launched the official conference with a call to "re-create" and "re-engineer" Kenya.

He drew a parallel with the United States' new start under Barack Obama but urged against revolutionary tendencies.

"The story of President Obama must indeed inspire us ... (But) the temptation to paint our existing institutions as having failed is strong, and some may have a powerful desire to tear down and replace them with new ones," he said.

"Americans did not tear down their institutions in order to place a black American in the White House. They worked within the existing institutions."

Kibaki presides over a coalition government set up in April, 2008, after a disputed presidential election touched off the worst violence in Kenya's post-independence history. More than 1,300 people died, and agriculture and tourism took a big hit.

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