* Communist walkout leaves Lupu backers short of votes

* Ex-Soviet state faces more uncertainty

* Another parliamentary vote seen in December (Adds quotes, background)

CHISINAU, Nov 10 (Reuters) - Moldova faced further political instability after a walkout by communists in parliament on Tuesday blocked the election of the pro-Western coalition's candidate as state president.

The vote for president -- for which Marian Lupu was the only candidate -- was the latest attempt by the governing Alliance for European Integration to tighten its grip on the ex-Soviet state after defeating the communists in a July poll.

But the opposition communists, denouncing proceedings as a "political farce", stymied the election of Lupu, a communist defector, by leaving the chamber before the ballot.

This condemned the 53 Alliance deputies to taking part in a doomed ballot since they were eight short of the 61 votes required for a president to be elected.

Former communist President Vladimir Voronin has publicly ruled out voting for Lupu, 43, whom he labelled as "a traitor".

But there are dissidents within communist ranks who may be ready to support him in exchange for political concessions and acting president Mihai Ghimpu said he was confident Lupu would be elected next time round. "We have to organise repeat elections for president and I am sure that Marian Lupu will become that president," he was quoted as saying by RIA Novosti.