LONDON - U.S. Secretary of State Condoleezza Rice said the NATO-led military mission in Afghanistan is "bumpy,'' and the international aid effort needs firmer co-ordination among the many countries participating.

Rice, who was to hold meetings on Afghanistan strategy in Britain on Wednesday, also said she hopes a new candidate will be chosen quickly for the job of overall international co-ordinator of aid, government and economic projects in Afghanistan. A respected British diplomat had accepted the position but backed out because of objections from Afghan President Hamid Karzai.

The choice for the job would probably be a European, not an American, Rice said.

The United States is also seeking to bridge a rift among NATO allies participating in unequal measure in Afghanistan.

"It's bumpy and it's a lot of maturing that the alliance is having to do to do this,'' Rice told reporters.

Some major European allies failed to send a significant number of troops to the southern front lines, leaving troops from Canada, the United States, Britain and the Netherlands to bear the brunt of a resurgence of Taliban violence in the region. Canada has threatened to pull out by February 2009 unless other allies do more of the hard work.

"It's true and we've made no secret about it that there are certain allies that are in more dangerous parts of the country and we believe very strongly that there ought to be a sharing of that burden throughout the alliance,'' Rice told reporters. "That said, I think we ought not to also dismiss the contributions that are being made by all alliance members.''

The U.S. contributes a third of NATO's 42,000-strong International Security Assistance Force mission, making it the largest participant, on top of the 12,000 to 13,000 American troops operating independently. The U.S. plans to send an extra 3,200 marines to Afghanistan this spring, including 2,200 combat troops to help the NATO-led force in the south.

Britain has about 7,700 soldiers in Afghanistan, up from 3,600 in 2006. Canada has about 2,500 troops in Afghanistan.

British diplomat Paddy Ashdown quit before he started as a so-called "super envoy,'' saying last month that Karzai had yanked his support.

UN Secretary-General Ban Ki-moon had asked Ashdown, who was Bosnia-Herzegovina's postwar international administrator, to do a similar job in Afghanistan.

Foreign ministers representing NATO countries have discussed combining the roles of the current civilian representatives of the UN, NATO and the European Union in Kabul into a single role. British officials had said Ashdown would be ideal because he had respect in world capitals.

The Afghan role would have been more limited than Ashdown's work in Bosnia, where he had sweeping powers. But he might have been too strong a figure for Karzai, whose government is widely seen as weak.

"There's still a desire to have an international figure who can better co-ordinate the international effort,'' and Afghanistan's U.S.-backed government is on board, Rice said.

"We'll take a look at the job description... but we want to be very clear this is a sovereign Afghan government and it has to take its own decisions, but it has a heavy reliance on international support.''

Rice said NATO allies were examining whether plans for the future size of Afghanistan's police and army forces were sufficient to fight the continued threat from the Taliban and other insurgent fighters.

Days after a retired U.S. general called Afghanistan a state at risk of failure, Rice said Karzai's democratic government is not threatened by a resurgent Taliban.

"You're not looking at a traditional military force that I think is a strategic threat to the government, but it is certainly causing insecurity for the population and that is something that is going to have to be dealt with,'' Rice said.

An independent study co-chaired by retired Marine Corps Gen. James Jones and former UN ambassador Thomas Pickering warned that the United States risks losing "the forgotten war.'' It pointed to deteriorating international support and the growing Taliban insurgency.

The Taliban launched more than 140 suicide missions last year, the most since the regime was ousted from power in late 2001 by the U.S.-led invasion that followed the Sept. 11 attacks on New York and Washington.