Canada's defence minister said he understands the frustrations of U.S. Defence Secretary Robert Gates when it comes to sharing the burden of NATO, adding that Canada does not want to see a "two-tier NATO."

In his final policy speech abroad as Pentagon chief Friday, Gates questioned the viability of NATO, saying its members' penny-pinching and lack of political will could hasten the end of U.S. support.

"Future U.S. political leaders — those for whom the Cold War was not the formative experience that it was for me — may not consider the return on America's investment in NATO worth the cost," Gates told a European think-tank on the final day of an 11-day overseas journey.

Gates' blunt assessment of the alliance didn't come as a surprise to MacKay.

"I've sensed Secretary Gates' frustration for some time about burden-sharing and the need to have 28 members of the alliance participating more actively and more fully," he told reporters at the Conservative convention in Ottawa Friday.

Question of the day

Is NATO obsolete?

"I just came from a meeting [of NATO in Brussels] — I've never seen him more adamant, going so far as to name names, and saying 'look we need some countries to step up'," MacKay said.

"Burden-sharing is a serious issue...we don't want to have a two-tier NATO. We want to know that countries are doing their all, participating in a way that is meaningful," MacKay said. "Obviously certain countries have more ability to do so, they have more equipment, more forces, more capacity, but we need to encourage countries to ensure that we're making a global effort."

Gates has made no secret of his frustration with NATO bureaucracy and the huge restrictions many European governments placed on their military participation in the Afghanistan war. He ruffled NATO feathers early in his tenure with a direct challenge to allied nations to contribute more front-line troops that yielded few results.

The North Atlantic Treaty Organization was formed in 1949 as a U.S.-led bulwark against Soviet aggression, but in the post-Cold War era its purpose has been questioned.

But recently, NATO has taken the lead in the Afghan war and the UN-mandated no-fly zone over Libya.

MacKay said the alliance is undertaking reforms to help streamline the deployment of expeditionary forces in conflicts such as Afghanistan and Libya, "that take us outside of our own territorial boundaries."

"So this is a new process when it comes to NATO's participation in these global conflicts, but it is one that I think Secretary Gates has been adamant about and consistent throughout his time."

MacKay also praised Gates for his leadership on the international stage and his efforts to visit NATO troops and set an example for NATO participation.

Canada pulling out of NATO program

Gates' comments about NATO partners not pulling their weight and contributing enough to sustain the alliance come as Canada prepares to withdraw from a key NATO program because of budget cuts.

CBC News  reported Thursday  that Canada intends to pull out of the Airborne Warning And Control System (AWACS), a series of military airborne surveillance and mission control planes that provides NATO with the ability to monitor air space, and to control fighter aircraft patrolling the skies.

The cuts have not yet been publicly announced, but sources told CBC News that MacKay raised the issue with some allies at a NATO conference in Brussels earlier this week.

The planes have been in heavy use in the Libyan campaign, monitoring the skies above the war-torn country, and guiding fighter planes towards their targets.

It's not clear when Canada will end its participation in the program, but sources report the decision has apparently angered some allies.

A NATO source told CBC that the AWACS program has never been busier than it is now and that it's viewed as a shining example of international military co-operation.

But the comments by Gates on Friday were not directed at Canada; rather he referred to the role of some European nations in the partnership.

Without mentioning specific countries by name, he blasted allies who are "willing and eager for American taxpayers to assume the growing security burden left by reductions in European defense budgets."

He cited Canada as an example of a NATO country that is making a credible contribution to the Libyan mission with constrained resources.

"The blunt reality is that there will be dwindling appetite and patience in the U.S. Congress — and in the American body politic writ large — to expend increasingly precious funds on behalf of nations that are apparently unwilling to devote the necessary resources or make the necessary changes to be serious and capable partners in their own defense," he said.

Gates is retiring on June 30 after leading the Pentagon for nearly five years.

With files from The Associated Press