By Andrew Heavens

KHARTOUM, Dec 07 (Reuters) - Sudan's key census results will not be released until at least February, its organiser said on Sunday, a hold-up that raises fears for the timing of coming elections.

The census is a cornerstone of a 2005 peace deal that ended two decades of north-south civil war, and will define the constituencies for the country's first democratic poll in more than twenty years, promised before July 2009.

But the Director General of Sudan's Central Bureau of Statistics Yasin Haj Abdin told reporters a series of technical problems meant the census findings from northern Sudan would not be ready for release until at least the second week in February.

Abdin said there had never been a formal deadline for publishing the census results. But at the time of the survey in April, government officials repeatedly said the findings should be available by September at the latest. That date was later extended to the end of the year.

Sudan expert Alex de Waal told reporters organisers would struggle to stage a proper election only a few months after the release of census figures.

"A huge amount of work needs to be done between the publication of the census results and holding the election," he said.

"It would be an extraordinary effort to get to elections from the census within a couple of months," he added. "Essentially, technically, it couldn't be done. You would need to take a shortcut."

Abdin said the first set of census data to be released would include names, addresses and other details needed to demarcate constituencies and draw up an electoral roll.

"I hope we will provide (the presidency) with those results by the end of the second week in February. So by the third week they will have the results in hand," he said.

He added that he could not comment on the implications for the elections as that was a political issue.

Other data not needed for the election, including cultural details and family income, would not come out until June, he added.

Officials from southern Sudan had managed to process all their data on time by September, said Abdin.

But the northern side of the operation has hit technical problems -- not least the challenge of finding ways round U.S. trade sanctions on Sudan to buy the computer equipment needed to process the results.

Officials from southern Sudan have already suggested that the elections be delayed because of logistical problems and the start of the rainy season around July.

The 2005 Comprehensive Peace Agreement also promises a referendum on southern secession in 2011.

The deal ended Africa's longest civil war, a conflict complicated by religion, oil, ideology and ethnicity. It claimed 2 million lives and forced more than 4 million to flee their homes. (Editing by Andrew Roche)