(Adds quote from ZEC official, court petition, details)

By Nelson Banya

HARARE, April 13 (Reuters) - Zimbabwe's opposition MDC vowed on Sunday to challenge a partial recount it said was designed to help President Robert Mugabe rig an election which has raised fears of a military crackdown.

A two-week delay in releasing the results from Zimbabwe's March 29 presidential election has heightened tensions in the southern African nation, where the economy has collapsed.

Regional leaders held a summit in Lusaka and called for the rapid verification and release of poll results and urged Mugabe, who did not attend, to ensure a possible run-off would be held "in a secure environment".

The Zimbabwe Electoral Commission (ZEC) said on Sunday it had ordered vote recounts in 23 constituencies, raising uncertainty over the vote and the possibility that the ruling ZANU-PF could overturn its defeat in the parliamentary poll.

"Vote recounts have been indicated in respect of all four, council, house of assembly, senate and presidential elections," Utoile Silaigwana, ZEC deputy chief elections officer, told Reuters. He declined to give further details.

Movement for Democratic Change lawyer Selby Hwacha accused the ZEC of calling the recount to help ZANU-PF rig the poll and said the MDC would launch a legal challenge on Tuesday.

"What ZEC is now trying to do is to abuse the law in an attempt to start a new process at ZANU-PF's bidding. We will see how they play it out, but we will challenge it," he told Reuters.

Morgan Tsvangirai's MDC says it won the presidential and parliamentary election, and accuses Mugabe of rolling out military forces across Zimbabwe to try to extend his 28-year rule in a de facto coup.

The opposition and human rights organisations have accused Mugabe's ruling party of orchestrating a systematic post-election campaign of violence and intimidation while it buys time to rig the vote.

The government sought to ease concerns the military might intervene, saying troops would not be deployed to fight civilians over the vote.

"The soldiers are in the barracks where they belong because the country does not fully require their services in such a peaceful environment," Zimbabwe's Sunday Mail quoted Information Minister Sikhanyiso Ndlovu as saying.

"I believe everyone in the country is aware that there is no military junta."

Zimbabwe's generals occupy no official posts in its ruling party, but the heads of the army and security forces are thought to have been key planners in an emerging strategy for Mugabe, 84, to fight back after elections handed the former guerrilla commander his biggest defeat since taking power.

REGIONAL SUMMIT

No results have been released yet from the presidential vote but ZANU-PF says neither Mugabe nor Tsvangirai won the necessary absolute majority and a run-off will be necessary. The MDC has rejected both a recount and a runoff.

The MDC filed a petition on Friday to try and block the recount, said Hwacha. He said the High Court had issued an order to stop the ZEC from recounting 16 constituencies. The court has not confirmed this.

Mugabe has been unfazed by sanctions imposed by Western foes and regional leaders have failed to pressure him to enact political reforms. But the March 29 vote has created his biggest crisis since taking power in 1980, when he was hailed as a liberation hero.

Zimbabweans had hoped the poll would bring relief from a deepening economic crisis.

Instead, a political stalemate has deepened anxieties and there are no signs neighbouring states mediating between Mugabe and the opposition will come to their rescue.

The 14-nation Southern African Development Community (SADC) summit ran almost 10 hours over schedule and ended around 5 a.m. (0300 GMT). A senior Zambian official said the delay was caused by a disagreement among leaders over whether the post-election impasse should be called a crisis.

Zambian Foreign Minister Kabinga Pande, in response to questions, told reporters after the 13-hour summit: "It is not a crisis at all."

Thabo Mbeki, president of Zimbabwe's powerful neighbour South Africa, said after meeting Mugabe en route to the summit there was no crisis.

Zimbabwe has inflation of more than 100,000 percent -- the highest in the world -- an unemployment rate above 80 percent and chronic shortages of food and fuel. Millions have fled abroad, most of them to South Africa. (Additional reporting by Shapi Shacinda and Serena Chaudhry in Lusaka, and Cris Chinaka, Nelson Banya, Stella Mapenzauswa, and Muchena Zigomo; Writing by Michael Georgy, editing by Sue Thomas and Mary Gabriel)

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