The United States urged NATO allies to invest in a missile shield and avoid harmful budget cuts at a meeting of defence and foreign ministers clouded by the war in Afghanistan.

US Secretary of State Hillary Clinton and Defence Secretary Robert Gates made the plea, echoed by NATO Secretary General Anders Fogh Rasmussen, amid French reservations about the anti-missile system.

"The studies have been done, the data are well-known and the affordability is clear," Gates told alliance ministers. "It is time for a decision."

The ministers gathered at NATO headquarters to discuss a new "strategic concept" that will shape the 28-nation alliance's vision for the next decade to face new threats including missiles from "rogue" states and cyber assaults.

Gates has put the price tag to link NATO members into a common anti-missile network at between 85 million and 100 million euros (120 million and 140 million dollars). Rasmussen says it would cost less than 200 million euros.

Rasmussen expressed optimism that the missile shield would be endorsed by NATO leaders at a summit in Lisbon on November 19-20, saying it was well on the way to a "consensus" following the ministerial meeting.

French Defence Minister Herve Morin, however, expressed his "reservations" about the plan, saying Paris wanted more details about how much the system would cost and how it would work.

But he hinted that France would not block the missile shield plan when NATO leaders meet in Lisbon.

France, a nuclear-armed power, was also at odds with Germany, which backs the missile shield plan but is also pushing for nuclear disarmament, diplomats said.

"We all agree that we need an anti-missile shield if we look at the threats of today and tomorrow," German Defence Minister Karl-Theodor zu Guttenberg told reporters. "We are very close to an agreement."

Clinton said the draft strategic concept recognises the need for NATO "to remain a nuclear alliance as long as nuclear weapons exist" and at the same time highlights President Barack Obama's goal of a nuclear-free world.

She also warned that plans to slash Britain's military spending could damage the military alliance.

In comments to the BBC, Clinton said in answer to a question that she was worried by defence cuts in Europe -- and specifically Britain.

"NATO has been the most successful alliance for defensive purposes in the history of the world I guess, but it has to be maintained," she said. "Each country has to be able to make its appropriate contributions."

Although Afghanistan was not officially on the agenda, ministers discussed the nine-year-old campaign which involves 150,000 international troops.

"Both Bob and I and a lot of our counterparts here in Brussels have both seen and received reports of progress that we are making on the ground," Clinton told a news conference.

Rasmussen also said the NATO-led force was willing to provide "practical assistance" to reconciliation efforts between the Afghan government and the Taliban but ruled out halting military operations against the insurgency.

NATO leaders are expected to endorse at a summit in Lisbon next month plans to begin the handover of security responsibility to Afghan forces by July 2011.

They will also sign off on the strategic concept, replacing a document written in 1999, two years before the September 11 attacks on the United States that sparked the war in Afghanistan..

The 11-page mission statement, drafted by Rasmussen, has not been made public but it is expected to touch on 21st century threats including cyber attacks, missiles from "rogue" states, terrorism and Somali piracy.

While Gates acknowledged fiscal pressures on defence budgets across the alliance, he warned against cuts that could weaken NATO and even leave it crippled.

"But as nations deal with their economic problems, we must guard against the hollowing out of alliance military capability by spending reductions that cut too far into muscle," he said.