(Adds U.N. envoy to Zimbabwe, paragraphs 4, 10-11)

By Nelson Banya

HARARE, Sept 19 (Reuters) - Zimbabwe's ruling ZANU-PF and the opposition Movement for Democratic Change failed again to break a deadlock over forming a Cabinet after reaching a power-sharing deal, an MDC spokesman said on Friday.

"After the meeting of the negotiators last night, there has been no shift and the deadlock has not been broken. What we want is genuine power-sharing, not a false marriage," MDC spokesman Nelson Chamisa said.

"The issue is about ZANU-PF not appreciating that this is not an exclusive ZANU-PF government. They want all the ministries and we obviously can't countenance that."

U.N. special envoy to Zimbabwe Haile Menkerios told reporters in New York the parties had asked the mediating team led by South African President Thabo Mbeki, who brokered the power-sharing agreement, to help resolve the new dispute.

President Robert Mugabe signed the agreement with MDC leader Morgan Tsvangirai on Monday, relinquishing some powers for the first time in nearly three decades of rule under pressure from regional leaders and a growing economic crisis.

They met on Thursday to try to sort out who gets which posts in the Cabinet.

The deal with Tsvangirai and the head of a breakaway opposition faction followed weeks of tense negotiations to end a political crisis compounded by the veteran leader's disputed and unopposed re-election in a widely condemned vote in June.

Marian Tupy, a policy analyst with the Cato Institute foundation in Washington, said the agreement would only succeed if both sides compromised.

"It now appears that Mugabe and ZANU-PF were never serious about giving up significant degree of power to the opposition. The international community would be well-advised to adopt a wait-and-see position," he said.

"HICCUP"

Menkerios briefed the U.N. Security Council on the power-sharing agreement. He described the disagreement between the MDC and ZANU-PF as a "snag" and a "hiccup."

"More difficult issues have been resolved before," he told reporters after the council meeting. "I believe it is possible to resolve this as well."

Under the agreement, Tsvangirai, who heads the largest of the two MDC factions, would become prime minister and chair a council of ministers supervising the Cabinet.

Tsvangirai's party is expected to get 13 Cabinet posts, with Arthur Mutambara's breakaway faction likely to control an additional three ministries.

Mugabe's ZANU-PF, which lost control of parliament in the March election for the first time in 28 years, is likely to have 15 ministers in the Cabinet.

But the 84-year-old Zimbabwean ruler, who has governed since independence from Britain in 1980, will retain the presidency, head the Cabinet and keep control of the powerful army. The police are expected to fall under the opposition.

Zimbabweans hope the agreement will be a first step in helping to rescue the once prosperous nation from economic collapse. (Additional reporting by Louis Charbonneau at the United Nations; Writing by Michael Georgy; Editing by Angus MacSwan and Peter Cooney)

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