HARARE,  (Reuters) - Zimbabwe's President Robert Mugabe turned 88 on Tuesday, joking about reports circulating for years of his imminent demise and vowing to stay in power despite international condemnation of his economic and human rights record.

Mugabe said he was in tip-top shape in an interview with state radio, and made no reference to media reports that he is receiving treatment for prostate cancer in Singapore.

"I have died many times. That's where I have beaten Christ. Christ died once and resurrected once," the devout Catholic Mugabe told the radio broadcaster.

"I am as fit as a fiddle."

Mugabe charmed world leaders with his wit and intellect in the early years of his rule, when a relatively rich Zimbabwe was praised for its education and social systems.

But he has since become a pariah in the West, blamed for running the economy into the ground and for massive human rights abuses to keep his grip on power.

Mugabe, one of Africa's longest-serving leaders, said his party ZANU-PF would choose his successor at the right time, but he had no intention of stepping down for now.

"Our members of the party will certainly select someone once I say I am now retiring, but not yet," he said in a separate interview with state TV.

"At this age I can still go some distance, can't I," Mugabe said, laughing, clapping his hands and rocking in his chair.

Asked whether his party still had anything more to offer after more than three decades in power, Mugabe said ZANU-PF's signature policies remained the defence of political independence and the pursuit of black economic empowerment.

Critics say ZANU-PF has helped ruin one of Africa's most promising economies with its seizures and distribution of white-owned commercial farms, and its more recent drive to force foreign-owned firms to transfer majority shareholdings to Zimbabweans.

Mugabe has shared power with his long-time foe, Prime Minister Morgan Tsvangirai, over the last three years after violent and disputed elections in 2008.

Mugabe has been nominated as ZANU-PF party's candidate and intends to run in an election he wants held this year. That would be a year ahead of schedule under the power-sharing deal which also calls for a new constitution to be drawn up and approved ahead of the poll.

"It's not a secret that there is grumbling in the party over his decision to go on and on, but those seeking to succeed him are not strong enough to challenge him," said Eldred Masunungure, a political science professor at the University of Zimbabwe.

"They are stuck with him for better or worse, and the attitude in ZANU-PF appears to be - lets hope for the best," Masunungure said.

A June 2008 U.S. diplomatic cable released by WikiLeaks last year said Mugabe had prostate cancer that had spread to other organs. His doctor urged him to step down in 2008, according to the cable.

Mugabe, who has ruled the southern African state since its independence from Britain in 1980, chaired a cabinet meeting on Tuesday.

Presidential officials said he would celebrate his birthday at a family dinner at his home in Harare. ZANU-PF is planning a celebration rally in eastern Zimbabwe on Saturday. (Editing by Jon Herskovitz and Andrew Heavens)