* Election limbo holds up signature of legal accord
* Without accord, NATO cannot stay beyond this year
* Rasmussen says "tough decisions" have to be made soon
By Adrian Croft
BRUSSELS, Aug 11 (Reuters) - NATO will soon be forced to take a decision on a total pullout from Afghanistan unless a deadlock over the country's election ends and a new president signs an agreement allowing foreign forces to stay, the head of the alliance said on Monday.
Secretary-General Anders Fogh Rasmussen told Reuters the Sept. 4-5 NATO summit in Wales would be very close to a deadline for taking that decision.
"Soon we will have to take tough decisions because if there isn't a legal basis for our continued presence in Afghanistan, we will have to withdraw everything by the end of this year and to do that we will have to start planning ... very soon," he said, without giving a firm date.
NATO will end its combat mission in Afghanistan by the end of this year but plans to leave behind a smaller force to train and advise Afghan security forces in their fight against Taliban insurgents.
To stay beyond 2014, NATO says it needs the Afghan government to sign agreements with the United States and NATO providing a legal basis for foreign troops to stay.
Afghan President Hamid Karzai has refused to sign the agreement with the United States. The candidates to succeed him - Ashraf Ghani and Abdullah Abdullah - say they would sign the agreements but they dispute the result of a run-off vote held in June and it could be weeks before a new president is installed.
The delays in signing the accords have sharply reduced the time available for detailed planning of the post-2014 mission, causing anxiety at NATO headquarters, and Rasmussen indicated that the situation was now becoming critical.
"Time is now of the essence and that is why we urge the Afghans to find a rapid conclusion of the presidential election process and we urge the new president to sign the legal arrangements as soon as possible after inauguration," he said.
With Afghanistan recounting some 8 million ballots cast in the June run-off vote, and amid allegations by Abdullah of widespread fraud, there have been fears that the formation of a proposed unity government could drag on for months.
However, both candidates have now signed an agreement stating that they will agree to a timeline for the electoral process and an inauguration date for the next president by the end of August.
The NATO-led International Security Assistance Force in Afghanistan currently numbers around 44,000 troops, including more than 30,000 Americans, according to the ISAF website.
U.S. President Barack Obama outlined a plan in May to withdraw all but 9,800 American troops by the end of the year and pull out the rest by the end of 2016, ending more than a decade of military engagement triggered by the Sept. 11 attacks on the United States in 2001.
About 4,000 troops from other NATO nations were expected to stay on beyond 2014 to participate in the training mission.
The Afghan presidential election limbo has created uncertainty over who, if anyone, will represent Afghanistan at the NATO summit, which will symbolically lower the curtain on NATO's years of combat in Afghanistan.
(Editing by Janet Lawrence)