By Patrick Worsnip

UNITED NATIONS, March 6 (Reuters) - U.N. peacekeeping chief Jean-Marie Guehenno, who has overseen the doubling of the world body's peacekeeping forces in eight years in the job, will quit the post later this year, U.N. officials said on Thursday.

Guehenno, a 58-year-old French career diplomat, told U.N. staff on Thursday he would be leaving soon after his current contract expires at the end of June, the officials said.

During his tenure -- longer than that of any of his predecessors -- the number of blue-hatted U.N. troops around the world has grown from some 50,000 to over 100,000 and the peacekeeping budget from $2.5 billion to $7.5 billion.

New missions were sent to Liberia, Ivory Coast, Haiti, Sudan and East Timor.

Perhaps the most challenging deployment is the one the United Nations began this year together with the African Union in the violence-torn western Sudanese region of Darfur. It will eventually consist of 26,000 troops and police, the largest such mission in the world.

Despite a normally low-key manner, Guehenno has in recent months made several hard-hitting reports to the Security Council, criticizing both Khartoum for obstructing the Darfur mission and U.N. members for failing to supply equipment.

U.N. officials say that while he was at the helm, peacekeeping changed from merely placing U.N. troops between armies that had stopped fighting to sending them into messy continuing conflicts like those in Darfur or the Democratic Republic of Congo.

In the 1990s, the U.N. peacekeeping department had been heavily criticized for failing to stop massacres in Bosnia and Rwanda.

U.N. officials offered little explanation as to why Guehenno was leaving this year, except to say he felt "this is a good time to move on."

Guehenno has been the most visible French national within the U.N. structure and U.N. sources suggested France would fight to keep the high-profile job, although the United States, Britain and other major powers might also be interested.

(Editing by Eric Beech)

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