By Ed Cropley

HARARE (Reuters) - Zimbabwe Prime Minister Morgan Tsvangirai vowed to pack entrenched President Robert Mugabe off into retirement at a thunderous final campaign rally on Monday, capping a high-spirited election race that has gone down to the wire.

With no reliable opinion polls, it is hard to say whether 61-year-old Tsvangirai will succeed on Wednesday in his third attempt to unseat his 89-year-old rival, who has run the southern African nation since independence from Britain in 1980.

To judge by the vociferous support for Tsvangirai's Movement for Democratic Change (MDC) and Mugabe's joking references to his own chances of success in Harare, the veteran president's ZANU-PF party is a long shot to take the capital in the vote.

The result hinges on whether Mugabe's control of the state media and security forces, the loyalty of independence war veterans and rural voters, and alleged irregularities with the voters' register, are enough to secure Africa's oldest leader another five years in power.

Speaking to 50,000 red-clad supporters in a Harare parade ground, Tsvangirai struck a conciliatory note towards Mugabe, saying he was not after revenge or prosecution, despite the death of 200 MDC supporters in disputed polls in 2008.

"After all this is done, I want President Mugabe to enjoy his retirement in the peace and comfort of his home," Tsvangirai told the crowd. "It's time for new blood and new ideas."

In return, MDC supporters, some perched high in trees to get a better glimpse, chanted "Bye Bye, Mugabe, we'll miss you". Many waved placards saying "89, 90, Game Over", a reference to the advanced years of the former guerrilla chief who led the fight against white minority rule in former Southern Rhodesia.

Mugabe receives regular medical treatment in Singapore, but denies reports he has been suffering from prostate cancer.

"CRY BABY"

The elections bring the curtain down on four years of fractious unity government brokered by South Africa and other countries in the region after the violence-marred 2008 poll.

Around 6.4 million people, almost half the population, are registered to vote although critics say the list is riddled with irregularities such as legions of dead people and, in some areas, more voters than residents.

At his final rally on Sunday, Mugabe dismissed Tsvangirai's charges of ZANU-PF vote rigging as the unfounded complaints of a "political cry baby", warning him to respect laws giving only the Zimbabwe Election Commission the power to announce results.

"I can tell you in advance that if you breach the law and become a law breaker, the police will arrest you," he said to cheers from thousands of supporters at a Harare stadium.

The election law says the results of the parliamentary and presidential vote should be known by August 5, although it is likely to come well before that.

Western observers are barred but the African Union and Southern African Development Community have nearly 500 monitors between them. More than 7,000 domestic observers are also accredited and tallies are to be posted outside each of the 9,735 polling stations in a bid to prevent vote-rigging.

Despite the extra transparency and greater use of technology such as mobile phones and the Internet, Tsvangirai supporters were resigned to the prospect of post-poll shenanigans, although they said the overall result was not under threat.

"The MDC always wins and then ZANU-PF steals it," said Saxon, a 32-year-old engineer, who did not want to give his family name for fear of reprisals. "But this time they won't get away with it."

After chaotic early voting for 70,000 police and civil servants, South African President Jacob Zuma's top Zimbabwe envoy said preparations for the poll were "not looking good", unusually strong words from Zimbabwe's powerful neighbor.

The United States and Britain have also voiced concerns, suggesting they are in no mood to lift the anti-Mugabe sanctions that prevent Harare normalizing relations with the International Monetary Fund and World Bank.

Mugabe, who has depicted Tsvangirai as a puppet of the West, accused Washington of being "absolutely insane".

Easing sanctions is seen as critical to getting Zimbabwe's economy back on track after a decade-long economic meltdown until 2009, blamed on Mugabe policies such as the seizure of white-owned commercial farms.

The precipitous decline, which included hyperinflation of 500 billion percent, only ended when the unity government scrapped the worthless Zimbabwe dollar. But despite some improvement from agriculture and diamond mining, the economy is struggling to take off due to lack of investment capital.

One of Tsvangirai's top election officials was arrested at the weekend on charges of tampering with ballot papers, a move unlikely to soften Western criticism that the run-up to the polls has been short of 'free and fair'.

(Reporting by Ed Cropley; Editing by Paul Taylor)