UPDATE 2-RWE in landmark win over Gazprom crucial contract clause

* First court verdict to thwart Gazprom's take-or-pay claim

* Newswire reports of $500 million claim

* Gazprom paid $2.5 bln to European firms as part of pricing deal

* To pay further 1 billion euros

* Gazprom is fighting off similar claim by Poland's PGNiG

(Recasts, adds analyst comments, agency report of $500 mln claim thwarted)

PRAGUE/MOSCOW, Oct 24 (Reuters) - RWE Transgas, the Czech unit of Germany's RWE, has won a landmark dispute with Gazprom over gas contracts, after a court ruled for the first time that a company did not have to pay fines under a ``take-or-pay'' clause.

The verdict is likely to play into the hands of Gazprom's disgruntled clients in Europe who may follow RWE and challenge take-or-pay claims from the Russian giant under which they must buy a minimum amount of gas or pay fines.

A spokesman for RWE Transgas, the republic's dominant gas importer, said on Wednesday that the company had successfully fought off a claim from Gazprom in a court in Vienna.

``I can only confirm that RWE Transgas is the winner against Gazprom in the take-or-pay dispute over long-term contracts,'' RWE Transgas spokesman Martin Chalupsky told Reuters.

``We are pleased with the court's decision. It will reduce our financial burden resulting from the contract by triple digit million euros per year,'' he said in a further emailed statement.

A spokesman for Gazprom declined to comment. Interfax news agency, citing industry sources, said Gazprom tried to wrestle$500 million from RWE Transgas for failing to stick to the take-or-pay commitments in 2008-2011.

The verdict will deal another blow to Gazprom's business in Europe, where it covers a quarter of natural gas needs. Its European clients have long complained of high prices in Gazprom's long-term gas supply contracts.

``This is an unpleasant precedent for Gazprom, while it's a positive factor for its clients. An avalanche of similar cases involving Gazprom's counterparties can not be ruled out,'' Constantine Cherepanov, a USB analyst in Moscow, said.

The Russian state-owned company is the main or sole gas supplier for central and eastern European countries, including Bulgaria, Hungary, Poland and the Czech Republic.

Gazprom is already the subject of investigation by the European Commission over suspicions that it hindered the free-flow of supply across the continent. It has agreed to revise its contracts with several leading European clients, including Germany's utility E.ON.

The world's top gas producer has returned more than 78 billion roubles ($2.48 billion) to its European clients in the first quarter as part of the contract dispute settlement. Gazprom has to repay a further 1 billion euros by the end of the year.

It has also been fighting off similar claims by Polish gas monopoly PGNiG.

Ukraine, a transit route of Russian gas to Europe, had already stated that it will not buy the previously agreed amount of gas from Gazprom.

``Gazprom had to give in to other clients' claims. This could be the case again,'' UBS' Cherepanov said.

($1 = 31.4232 Russian roubles)

(Reporting by Michael Kahn in Prague; additional reporting by Denis Pinchuk in Moscow; editing by Jan Lopatka and William Hardy)