* Opposition parties say to form government
* Pick ex-rebel commander Haradinaj for PM
* Thaci's PDK won election, but without majority (Adds quotes, analyst, details)
By Fatos Bytyci
PRISTINA, June 10 (Reuters) - Three Kosovo opposition parties united on Tuesday to announce plans for a government to thwart Prime Minister Hashim Thaci's bid for a third term after he won an election but was left seeking coalition partners.
They put forward Ramush Haradinaj, a burly former guerrilla commander twice cleared of war crimes by a United Nations court, as their choice for prime minister for the next four years.
But it was not clear whether his Alliance for the Future of Kosovo (AAK), which struck the deal with two other parties, would legally be able to have the first try at forming a government rather than Thaci's Democratic Party of Kosovo (PDK).
"The constitution states clearly that the mandate to form the government belongs to the winner of the election, which in this case is the PDK," Thaci's party said in a statement.
"They are violating the constitution," said Deputy Prime Minister Hajredin Kuci, a close ally of Thaci. "This is pressure on us to raise the negotiating price."
The PDK came in first with 31 percent in Sunday's election marked by low turnout among Kosovars frustrated with poverty and corruption six years after seceding from Serbia.
Haradinaj's AAK said it had forged a coalition with the second-placed Democratic League of Kosovo (LDK) and a splinter party of defectors from Thaci's PDK.
"NO THACI THREE"
The leftist Self-Determination party, which came in third, said it would support the proposed coalition in parliament, though it left unclear whether it would formally join.
"There will be no Thaci Three government," party leader Albin Kurti told journalists.
Together, the three parties and the Self-Determination party took more than half the vote, but it could be weeks before the results are certified and parliament sits.
In a statement likely to infuriate Thaci's supporters, the parties said they had "decided to give the country a government that will restore hope."
Naim Rashiti, a Balkans Policy Research Group analyst, said the legal procedure for forming a government was unclear and predicted a conflict over interpretation of the constitution.
"This is more a coalition designed to bring down Hashim Thaci," he told Reuters. It remained to be see if Thaci will be able to win over at least one of the parties now opposed to him.
According to the opposition agreement, Haradinaj, who briefly served as prime minister in 2004-2005 before quitting to stand trial for war crimes in The Hague, would head the government.
He has twice been acquitted by the Hague-based United Nations tribunal for the former Yugoslavia on war crimes charges stemming from a Kosovo Albanian guerrilla insurgency in 1998-99, when NATO intervened with air strikes to halt the massacre and mass expulsion of ethnic Albanians by Serbian forces.
Kosovo became a ward of the United Nations and declared independence in 2008 with the backing of the West. (Writing by Matt Robinson; Editing by Tom Heneghan)