(Adds Canadian comments in paragraphs 11-12)

LONDON, Feb 11 (Reuters) - The reluctance of NATO allies to send more troops and resources to Afghanistan is jeopardizing the military mission there, the United States and Britain said on Monday.

British Foreign Secretary David Miliband said Afghanistan risked becoming a "failed state" unless more efforts were made to fight Islamic militants, and U.S. Undersecretary of State Nicholas Burns appealed for more help from Europeans.

U.S.-led forces toppled the Taliban government in 2001, but Taliban rebels launched an insurgency two years ago and violence has risen sharply since then.

Miliband, who visited Afghanistan last week with U.S. Secretary of State Condoleezza Rice, said it was vital other NATO members increase their commitment.

"It would help precipitate even more dangerous insecurity in Afghanistan (if the international community pulled out)," Miliband told BBC radio. "If more effort is not made, Afghanistan risks becoming a 'failed state.'"

"We do need the whole of the international community, including European countries, to step up," he said.

Burns, speaking ahead of talks with British officials on Afghanistan and other areas of foreign policy, said it was unfair that a few NATO members -- mentioning the Americans, British, Dutch and Canadians -- were shouldering the burden.

"It is incumbent on us to say, with great respect, we need help from Germany and the other major west European countries," he told reporters, when asked about Germany's involvement.

"It's hard to think of a successful military operation when the majority of the capitals are saying we decide where and when the troops are deployed," he said.

He referred to the large number of Canadian casualties, adding: "For Canada to do all that and not have the support of every country in the alliance to come and help with resupply, with helicopters, with combat troops, is not a recipe for success."

In Canada, Defence Minister Peter MacKay said that while he did not think "we're nearing any sort of a crumbling or a collapse of the Alliance," the response from NATO would reflect its ability to conduct major missions.

"We share the view that other countries have to come to the fold. And part of that is (showing) a willingness to make these difficult, tough sacrifices in a military mission such as this," he told the Canadian Broadcasting Corp.

Burns said he believed NATO's mission was heading "in the right direction" and would ultimately defeat the Taliban.

France has indicated a willingness to send more troops, but Germany has been adamant it cannot do more.

Britain, the second largest contributor to the 43,000-strong ISAF international peace force, is feeling intense pressure as its 7,000 soldiers -- based mostly in southern Helmand province -- battle increasingly fierce resistance and casualties rise.

Aside from the military campaign, Miliband and Burns stressed the need for greater effort on the civilian side.

Burns said he was worried that the civilian effort had been "disjointed" and hoped the appointment of a new United Nations envoy could help coordinate this. Afghan President Hamid Karzai rejected Britain's Paddy Ashdown for the role. (Reporting by Katherine Baldwin and Kate Kelland in London and David Ljunggren in Ottawa; Editing by Tim Pearce)

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