By Patrick Worsnip

UNITED NATIONS, Sept 23 (Reuters) - U.N. Secretary-General Ban Ki-moon sought increased backing on Sunday for efforts to impose peace and order in Afghanistan from representatives of key countries involved there.

Afghan President Hamid Karzai and foreign ministers and U.N. envoys from 17 other nations gathered at U.N. headquarters in the latest of a series of meetings before Tuesday's opening of the annual General Assembly gathering of world leaders.

Since U.S.-backed forces overthrew Afghanistan's Taliban rulers in late 2001, Karzai's government has struggled to keep control, faced with a resurgent Taliban, independent-minded warlords and rising drug production.

About 50,000 foreign troops are deployed there, including a NATO-led International Security Assistance Force, or ISAF, and separately led U.S. forces.

A U.N. mission supports and advises the Afghan authorities on economic and political development, justice reform, humanitarian aid and anti-drug programs.

"If I expect one thing to come out of this meeting, it is that they reinforce the commitment to Afghanistan," U.N. Afghanistan envoy Tom Koenigs said of the session attended by the country's neighbors and key NATO states.

"We need more troops, we need more money and we need a sustainable commitment in Afghanistan," he said on Friday

Diplomats, however, said Sunday's meeting was not expected to result in specific pledges.

Western countries have been pressing for the United Nations to boost its profile in Afghanistan after Koenigs quits at the end of this year.

U.N. officials said, however, that Ban would say he would not expand the U.N. mission until there were sufficient security guarantees -- a reference to continuing fighting in the south.

Koenigs said the Taliban insurgency could not be defeated by military means alone.

"There must be a comprehensive strategy which comprises civilian and military action, so we come to a political offensive against the insurgency," he said.

An Afghan presidential spokesman said last week Kabul was ready for peace talks with the Taliban but would not accept preconditions demanded by the Islamist rebels, such as the withdrawal of all foreign troops.

The Afghan meeting is the latest of several Ban has convened to underscore the central U.N. role. Ministers discussed Darfur on Friday and Iraq on Saturday. A meeting of Middle East mediators was scheduled for later on Sunday and a major conference on climate change will be held on Monday.

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