KHARTOUM (Reuters) - Sudan on Friday rejected a suggestion by U.N. Secretary-General Kofi Annan that the United States and Europe help set up a possible mobile force in Darfur to supplement African troops now on the ground.

"We think that the African Union is doing a good job and so far they have not said they are unable to do that job," Foreign Minister Lam Akol told Reuters.

"Naturally what should happen is to give them the money they want, not to complicate matters by involving another force on the ground," he said.

But the U.N. special envoy Jan Pronk said it was premature for Khartoum to react since the African Union and the U.N. Security Council had not yet made a decision.

"The Government of Sudan will have to think and take a position. My advice to each and everybody is to not listen to the first reaction of the Sudanese government," he told a news conference at the United Nations in New York.

"The government in the past starts out with a negative position, which later ends up positive," Pronk said. "The important thing is, what is the final position of the Sudanese government, and we have ample time to discuss that."

But Pronk said Darfur would need 12,000 to 20,000 troops, numbers higher than U.N. military officials are considering. He said soldiers were not only needed to quell fighting to guard people eager to leave squalid camps.

The United States supports augmenting African Union forces in Sudan's western Darfur region with U.N. peacekeepers but has not offered its own troops for such a mission.

LOGISTICAL SUPPORT

U.S. diplomats said Washington would be hard pushed to find enough troops to send into Darfur given its commitments in Iraq and Afghanistan. The U.S. contribution would likely be logistical support.

One of two main Darfur rebel groups, the Sudan Liberation Army (SLA), said it would welcome U.S. troops.

"If the Americans came they would be preferable to the African Union who so far have failed in their duties to protect civilians," SLA Vice President al-Raya Mahmoud Juma'a said.

"They (the African Union) have enough forces and equipment, but they still cannot do their job and stop the attacks," he told Reuters from Darfur.

The other group, the Justice and Equality Movement (JEM), said the nationality of the force did not matter, but said the AU force needed a stronger mandate and more troops.

The African Union has 7,000 peacekeeping troops in Darfur, a region the size of France, a limited mandate to use force and only enough funds until March. If it gets more money, it will leave troops in Darfur for another 9 to 12 months.

The AU depends on donor countries to fund its mission to monitor a tentative truce in the region, where violence has driven more than 2 million from their homes.

In a statement seen by Reuters Friday, the AU said it "expresses its support, in principle, to a transition from (AU) to a UN operation." It planned to meet before the end of March to decide on any future handover to the United Nations.

U.N. Secretary-General Kofi Annan said on Thursday the United Nations was drawing up contingency plans and most diplomats expect a U.N. takeover within a year.

Asked whether that would include rich countries like the United States and European nations, Annan said, "Those are the kind of countries with the kind of capabilities we will need, so when the time comes, we will be turning to them."

(Additional reporting by Tsegaye Tadesse in Addis Ababa, Sue Pleming in Washington, Evelyn Leopold at the United Nations.)