By Ross Colvin

BAGHDAD, Sept 4 (Reuters) - The buildup of U.S. troops in Iraq has reduced sectarian killings, but military success is not sustainable unless warring sects make progress towards national reconciliation, the United Nations mission chief said.

Ashraf Qazi, a veteran Pakistani diplomat coming to the end of a three-year stint in Iraq, was speaking on the day U.S. President George W. Bush made an unannounced visit to western Anbar province to get an assessment from his commanders.

Bush is heading to a showdown with the Democratic-controlled Congress over his Iraq strategy. Democrats say it is not working because Iraq's divided leaders have failed to take advantage of a troop buildup, or "surge", to reach a political accommodation.

"The impression one has here is that the surge has made a difference with regard to the security situation in Baghdad and in some western governorates ... The number of killings, disappearances and the daily dreadful quota of unidentified bodies has dropped considerably," Qazi said on Monday, giving his first public assessment of the strategy.

But that was to be expected given the sheer number of U.S. and Iraqi troops now deployed in the capital.

"The most important thing is to see how sustainable that is. That will depend on how much progress is made towards national reconciliation," he told Reuters in an interview in the heavily fortified United Nations compound in Baghdad's Green Zone.

Under Qazi, the United Nations mission, numbering about 50 people, has issued quarterly reports that have grimly detailed Iraq's spiral into sectarian violence. It has angered the Iraqi government over its publication of high death toll figures.

The mission's main political role in Iraq to date has been to assist in national elections in January and December 2005 and a referendum on the new constitution. But the Security Council last month voted to expand that role, to promote reconciliation between rival factions and dialogue with Iraq's neighbours.

"It is about time that we did move on ... We have not been as active in promoting national reconciliation as we might have been. The need to bring in the U.N. is now more apparent to more of the players," said Qazi, whose term in Iraq ends next month.

UN NEUTRAL, EXPERIENCED

The United States and Britain, which sponsored the Security Council resolution, have denied their aim is to offload Iraq's political problems onto the United Nations, at a time when the country is in political crisis and hundreds continue to die.

"I don't believe there is an unburdening or unloading on the U.N. In the beginning the challenge in Iraq appeared to be less complex than it has turned out to be," Qazi said.

"As things have developed, the complexity of the situation has become more apparent and the need for a more inclusive, broader approach -- the appreciation for that has grown over the past year," said Qazi, who served as Pakistan's ambassador to India, the United States, China and Russia.

"We do have comparative advantages. We are seen as being an impartial and neutral entity with vast experience," he said.

But a bomb blast that destroyed the U.N. office in Baghdad on Aug. 19, 2003, killing 22 people, including his predecessor Sergio Vieira de Mello, continues to haunt the mission.

Not surprisingly, United Nations Secretary General Ban Ki-moon has said an expansion of the mission will be subject to security concerns, after the U.N. Staff Union called on him not to send any more people to Iraq and to withdraw those there.

"Although we live in a high-risk environment, we have mitigated that risk down to an acceptable level ... We now have overhead protection and more secure accommodation and the necessary logistical and life support systems," said Qazi.

"It is still under review, but the likelihood is that if the security situation does not deteriorate further, we would have more people here."

He said there would be about 30 more staff. Most of the U.N. agencies are based in neighbouring Jordan. Qazi himself has been tipped as Ban's new envoy to Sudan.

(Editing by Ralph Boulton, Baghdad newsroom))

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