By Elias Biryabarema

KAMPALA (Reuters) - Uganda plans to withdraw by the end of the year troops involved in an operation to hunt down Lord's Resistance Army rebels in Central African Republic, a military spokesman said on Friday.

Uganda leads a U.S.-supported African Union regional task force tracking the LRA rebels, who are notorious for mutilating civilians and kidnapping children for use as fighters and sex slaves.

Most of its 2,500 troops are in eastern Central African Republic. A smaller contingent is based in South Sudan.

Spokesman Paddy Ankunda said the withdrawal did not mean Uganda was ending the operation. But while the African Union favored keeping the Ugandan troops in place, he said, Kampala had been discouraged by insufficient international support.

"There seems to be no serious goodwill on the part of international actors or stakeholders to participate or contribute toward the ending of the LRA problem," he said.

He added that Uganda had not yet considered an African Union request to maintain its troops in Central African Republic.

The International Criminal Court has issued arrest warrants for the LRA's messianic leader, Joseph Kony, and other senior commanders.

However, the brutal rebel movement was known to relatively few outside Central Africa until KONY 2012, a highly successful social media campaign, raised international awareness about the reclusive warlord four years ago.

Abdoulaye Batilly, U.N. Secretary-General Ban Ki-moon's special representative in Central Africa, acknowledged the strain on Ugandan resources, but warned the withdrawal must not allow for a rebel resurgence.

"With Uganda wanting to pull out, we must create conditions so that a vacuum is not created ... And we're discussing this with everyone, the European Union, the USA, and of course the government of CAR," he said, speaking in Central African Republic's capital, Bangui.

Though originally from northern Uganda, the LRA was driven out of the country by a military offensive a decade ago. Today, its fighters roam a poorly policed area straddling the borders between Central African Republic, Democratic Republic of Congo and South Sudan.

Those countries are also meant to contribute to the task force, but separate conflicts in Central African Republic and South Sudan have meant that the bulk of the operation has fallen to Ugandan troops.

General David Rodriguez, commander of the U.S. military's Africa Command, estimated in March that less than 200 LRA fighters remained.

"To defeat your enemy does not mean to kill all of them. It means to deny them the means to make war. And that's where we are with the LRA," Ankunda said.

However, finishing the group off once and for all has proved difficult. Its fighters continue to launch attacks on civilians, nearly 350 of whom have been abducted by the group this year, according to the LRA Crisis Tracker, which documents rebel attacks.

(Reporting by Elias Biryabarema; Additional reporting by Crispin Dembassa-Kette in Bangui; Writing by Makini Brice and Joe Bavier; Editing by Angus MacSwan)