By Cris Chinaka

HARARE, Aug 26 (Reuters) - Zimbabwean President Robert Mugabe is expected to open parliament on Tuesday after his ruling ZANU-PF and the opposition MDC won key positions in the chamber.

The opening of parliament could intensify a post-election political struggle between the two sides that has threatened to scupper power-sharing talks.

Zimbabwe's main opposition Movement for Democratic Change (MDC) party won the vote for parliament speaker, gaining one of the most powerful positions in Zimbabwean politics for the first time since independence in 1980 in a blow to Mugabe.

The MDC has protested against Mugabe's plans to open parliament, saying it would hamper talks on forming a unity government. The MDC speaker, Lovemore Moyo, could boycott the opening, causing embarrassment for Mugabe and raising doubts about whether the negotiations can continue.

Technically, if the speaker did not show up, the deputy speaker, who is from a breakaway MDC faction, would take his place and the parliament would open.

Morgan Tsvangirai's Movement for Democratic Change said it might attend the opening of parliament out of respect for the new speaker but it did not recognise Mugabe as the country's president.

ZANU-PF won a vote for the presidency of the upper house of parliament, the Senate -- where it has a majority -- meaning it can block legislation passed by parliament.

Negotiations between ZANU-PF and the MDC have stalled over what the opposition says is Mugabe's refusal to give up executive power after 28 years in office.

The deadlock, in spite of strong regional and international pressure for a deal, has dampened hopes of an agreement that could end the political crisis and revive the economy.

Political analysts say that although the talks on how to share power look doomed for now, they are likely to resume in the coming weeks because both Mugabe and Tsvangirai are under intense pressure to reach a settlement.

Arthur Mutambara, leader of the smaller, breakaway faction of the MDC, could emerge as the kingmaker.

Mugabe's party lost control of parliament in March elections for the first time since independence from Britain, winning 99 seats, but Tsvangirai's party only won 100 seats so does not have an absolute majority either.

That leaves control in the hands of Mutambara's breakaway faction, which has 10 seats. There is one independent. (Writing by Michael Georgy; Editing by Giles Elgood)

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