* Top court unblocks planned power plant investment
* Sends case for back for re-examination to lower court
* Treasury Minister says "good news" for builders
* Ecologists vow to file for block again
(Wraps PGE stories, adds PGE comment, updates shares)
By Maciej Onoszko
WARSAW, Oct 2 (Reuters) - Poland's top utility PGE said it would carry on with its 11.6 billion zloty ($3.7 billion) investment in new power units after a supreme court ruling unblocked the country's largest power contract to date.
The project, keenly awaited by local builders, has been shrouded in uncertainty since a provincial court blocked PGE's investment in two 900-megawatt coal-fired units after ecologists appealed against the granting of an environmental permit.
In a ruling on Tuesday, the supreme administrative court annulled that decision and sent the case back to the lower court for re-examination.
"The ruling passed today means that the environmental permit is valid," PGE said in a statement. "Therefore, PGE ... is continuing the investment process in the Opole power plant."
But environmental group ClientEarth, which appealed against the permit, warned it might still seek to block the project.
"We lost the battle, but we have not lost the war," said Marcin Stoczkiewicz, a board member of ClientEarth Poland.
State-controlled PGE has said more delays to the project in the southwestern city of Opole could hurt construction firms and deprive the slowing economy of an important cash stimulus.
Poland's construction sector is following the case closely as many major builders - strapped for cash after bidding for road deals pushed them to the brink of insolvency - are involved in the project.
"There is now a real chance to realise the investment," said Treasury Minister Mikolaj Budzanowski in a statement. "This is also good news for the construction sector. Polish firms will be able to carry out this investment using Polish technology."
The consortium to build Opole includes Polimex , Rafako , a unit of PBG , and Mostostal Warszawa , the Polish unit of Spanish firm Acciona .
PBG has been in bankruptcy protection since June, while Polimex has until Nov. 24 to come up with an austerity plan after its creditors agreed to waive interest on the group's 2.5 billion zloty debt pile in July.
Polish state development agency ARP said in September it would buy up to a third of Polimex Mostostal , left on a financial cliff-edge by unprofitable motorway contracts.
Shares in PGE were unchanged, while PBG had shot up almost 4 percent at 1448 GMT. Rafako and Mostostal each traded almost 3 percent higher, while Polimex closed 3.3 percent lower.
($1 = 3.1733 Polish zlotys)
(Additional reporting by Adrian Krajewski and Marcin Goettig; Editing by Catherine Evans)
Keywords: PGE COURT/