By Gabriel Partos BBC South-east Europe analyst

For the third time in just over a year the people of Serbia are voting in elections on Sunday for the republic's president.

As on previous occasions, the polls suggest the election is unlikely to produce a valid result - but Serbia's politicians are already focusing on the much more important forthcoming parliamentary elections.

Micunovic appealed for support of the election process

These will now be held at the end of December, following the dissolution of parliament on Thursday.

Serbia's most popular politician, Vojislav Kostunica, who three years ago defeated the authoritarian Slobodan Milosevic in the Yugoslav presidential contest, came first in each of the votes for the Serbian presidency last year.

But he was deprived of victory - because the ballots were declared invalid due to the turnout being less than half the electorate.

One of the main reasons why the turnout was insufficient, was that the governing DOS coalition discouraged its supporters from casting their ballots since it knew it could not stop Mr Kostunica - a one-time ally turned political opponent - from winning the presidential race.

Real power

This time it is Mr Kostunica, leader of the nationalist Democratic Party of Serbia (DSS), who is likely to scupper the vote for a new president.

"The Democratic Party of Serbia thinks these presidential elections don't make sense," he said.

"They are just prolonging the agony and decay of Serbia. That's the reason why the DSS is not inviting people to go to the polls."

For now, Sunday's vote is likely to be a useful test for both Prime Minister Zivkovic and Mr Kostunica of just how much support their parties enjoy in the run-up to the parliamentary elections

Mr Kostunica's dismissal of the presidential election came in response to an appeal from the DOS coalition's candidate, Dragoljub Micunovic, for an endorsement of the presidential election process.

But the last thing Mr Kostunica has wanted to ensure is that one of his DOS opponents, Mr Micunovic - the front-runner among the six candidates - wins the presidential race. After all, had he decided to stand, Mr Kostunica would almost certainly have come out on top again.

Instead, Mr Kostunica has been renewing his long-standing call for early parliamentary elections. That is because real power lies with the government, not with the presidency.

The beleaguered DOS coalition, which in recent days lost a further two of its smaller constituent parties, has now caved in.

On Thursday the acting President, Natasa Micic, announced the dissolution of parliament following the government's decision that early elections will be held on 28 December - a year ahead of schedule.

Key elections

Prime Minister Zoran Zivkovic may have agreed to meet Mr Kostunica's demand to avoid a humiliating defeat in an imminent vote of no-confidence in his government.

For his part, Mr Micunovic, who espoused the call for early elections, may now be hoping that in an eleventh-hour change of mind, Mr Kostunica may encourage his supporters to vote.

Some Serbs have signed a petition calling for early elections

But whether or not Sunday's vote is valid and Mr Micunovic is elected president, what really matters now are the forthcoming parliamentary elections.

And if the polls are correct, the elections are likely to produce an outcome which may well require a reconstitution of the grand coalition of DOS, its current opponent, the DSS, and the G-17 Plus group of technocrats which broke with the DOS government last year.

That was the coalition that had beaten Mr Milosevic's Socialists three years ago, raising many - so far unfulfilled - expectations of reform among Serbs.