US Defence Secretary Robert Gates shakes hands with Co-President of the Security and Defence Agenda (SDA) Jaap De Hoop Scheffer (L) prior to delivering a speech to the Security and Defence agenda think tank in Brussels (JASON REED/AFP/GETTY IMAGES)

Defense Secretary Robert M. Gates rebuked some of America’s staunchest allies Friday, saying the United States has a “dwindling appetite” to serve as the heavyweight partner in the military order that has underpinned the U.S. relationship with Europe since the end of World War II.

In an unusually stinging speech, made on his valedictory visit to Europe before he retires at the end of the month, Gates condemned European defense cuts and said the United States is tired of engaging in combat missions for those who “don’t want to share the risks and the costs.”

“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 ... to be serious and capable partners in their own defense,” he said in an address to a think tank in Brussels.

The speech comes as the United States prepares to begin withdrawing some of its forces from Afghanistan this summer and as it and other NATO powers engage in an air campaign against the forces of Libyan leader Moammar Gaddafi. In both cases, Gates said, budget cuts and sheer reluctance among European partners to fight have made the missions significantly more difficult and shifted the burden onto the United States.

The challenges facing the Libyan campaign were underscored just hours after Gates spoke, as Norway announced it would pull its forces out of operations by the beginning of August because of the burdens on its small military.

The country’s F-16 jets have carried out about 10 percent of the airstrikes on Libyan soil since the NATO operations began at the end of March, according to Norway’s air force.

This week, NATO carried out the most intensive bombardment of the Libyan capital, Tripoli, to date. But the airstrikes are depleting NATO munitions, forcing the United States to supply more, Gates said.

U.S. officials have been unhappy with Germany in the months since it refused to support a U.N. Security Council resolution to intervene in Libya, but President Obama feted German Chancellor Angela Merkel on Tuesday at the White House, presenting her with the Presidential Medal of Freedom.

In response to Gates’s speech, the German Foreign Ministry dismissed the notion that it was not sufficiently contributing to NATO and noted the celebrations earlier this week in Washington.

“Germany makes a considerable contribution to NATO and NATO-led operations,” said a Foreign Ministry spokeswoman, speaking anonymously under diplomatic ground rules. “Germany’s engagement is very emphatically valued,” as evidenced by Merkel’s new medal, she said.

Official reaction in other European capitals appeared muted Friday. The French Defense Ministry had no immediate comment.

But NATO Secretary General Anders Fogh Rasmussen shares Gates’s concerns about European willingness to contribute to its own defense, an alliance spokeswoman said. “There is clearly a long-standing concern about the transatlantic gap in defense spending,” Oana Lungescu told reporters in Brussels.

Gates’s criticism drew mixed reactions from European think tanks. Daniel Korski, a senior policy fellow at European Council on Foreign Relations said the speech displayed ignorance about widespread budget cuts across Europe. But Jonathan Eyal, director of international security studies at the Royal United Services Institute in London, said the departing U.S. defense chief delivered a message that Europeans need to hear.

In Libya, Gates said, “the mightiest military alliance in history is only 11 weeks into an operation against a poorly armed regime in a sparsely populated country, yet many allies are beginning to run short of munitions, requiring the U.S., once more, to make up the difference.”

Gates and other U.S. officials have criticized Europe in the past, saying it is failing to hold up its end of the bargain. But his harsh language Friday in the speech to the Security and Defense Agenda think tank — delivered after a NATO defense ministers’ summit in which NATO and American top brass tried but largely failed to secure additional resources for the Libyan campaign — was a sign of just how tenuous the military relationships have become.

“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,” he said.

Gates said he has “worried openly” in the past “about NATO turning into a two-tiered alliance between members who specialize in ‘soft’ humanitarian, development, peacekeeping and talking tasks and those conducting the ‘hard’ combat missions — between those willing and able to pay the price and bear the burdens of alliance commitments, and those who enjoy the benefits of NATO membership ... but don’t want to share the risks and the costs.”

“This is no longer a hypothetical worry,” Gates said. “We are there today. And it is unacceptable.”

Gates expressed alarm about “the real possibility for a dim, if not dismal, future for the transatlantic alliance.” He added: “Such a future is possible, but not inevitable. The good news is that the members of NATO — individually and collectively — have it well within their means to halt and reverse these trends and instead produce a very different future.”

Gates is stepping down as defense secretary on June 30 after more than four years in office. Obama has nominated CIA Director Leon E. Panetta to succeed him. Panetta’s Senate confirmation process started Thursday with testimony before the Armed Services Committee.

The global financial crisis has stretched the budgets of countries around the world, and even the U.S. defense budget, long immune to cuts, has seen its projections trimmed. But many countries in Europe have been quicker to reduce their forces. Last fall, Britain and France agreed to share an aircraft carrier. This spring, Germany eliminated its draft and slimmed the size of its ground forces. Smaller countries have made big cuts to forces that were never particularly large.

At a defense conference in Munich in February, Rasmussen, the NATO secretary general, made an impassioned plea for smarter spending, and more of it. Europe’s patchwork of small countries leads to a jumble of small military forces that are not particularly effective if they actually need to go to war, critics say.

Gates repeated the criticism on Friday, saying that the $300 billion that non-U.S. NATO members spend annually on defense “could buy a significant amount of usable military capability. Instead, the results are significantly less than the sum of the parts.”

He said that the best hope for NATO was for European leaders to push harder to protect their budgets from further cuts, and he urged them to work together to coordinate their military capabilities.

“It is not too late for Europe to get its defense institutions and security relationships on track,” Gates said.

Korski, a defense policy expert at the European Council on Foreign Relations, a pan-European think tank, complained after the speech that “we are getting used to upset defense secretaries spewing bile at regular intervals.” European governments “face dramatic budget pressures, and that means cuts in health, education and also defense,” he said, adding that “to assume that defense would be immune to the effort of balancing budgets is absurd.”

Korski rejected “the idea that everybody shares the same risk assessment” as the United States “and that everyone must show solidarity” with Washington. For example, “many Europeans, excluding the British, don’t regard Afghanistan as a threat,” he said, and Eastern Europeans do not feel the Americans show sufficient sympathy for their fears of Russia.

Eyal, of London’s Royal United Services Institute, said the speech would be “very welcome” in Britain and France, however, because “privately this is what officials have articulated for years.” Gates “identified the key problem, which remains Germany,” he said. “You can argue that there are many countries that do not contribute their fair share, but most of the others don’t matter, and smaller ones would likely fall into line if Germany did.”

Eyal said: “It’s a shame politicians say what they think only when they are about to depart, but the Europeans needed this cold shower, and if it’s up to Gates to administer it, so be it.”

The speech amounted to “an outburst of frustration that is bigger than bottom line of defense cuts,” he said. “It’s about the lethargic way the Europeans walk on the world stage,” lacking a sense of urgency and thinking that “at the end of the day the Americans will always be there and do Europe’s bidding.”

But the speech “hasn’t caused a great rift,” Eyal said. “Deep down, there is no one in Europe that doesn’t think that what Gates said is absolutely the truth. No one argues he’s exaggerating problem. It’s not a rift. It’s worse. It’s an act of indifference.” The missing reaction in Europe, he said, is to reconsider burden-sharing and “how the Europeans can contribute more to the common pot.”

In Germany, one analyst said that Gates’s reaction to European defense cuts was understandable even if he was overreacting to disagreements within NATO.

“The Europeans do not understand that they will have to take much greater care of their own security,” said Constanze Stelzenmueller, a Berlin-based fellow at the German Marshall Fund of the United States. “They haven’t translated that into their defense budgets.”

NATO members disagree not just about spending levels, but also about what constitutes a threat, Stelzenmueller said. However, she said, “it is to be expected, and in fact normal, for allies to disagree with each other on how to react” to situations such as that in Libya. “I don’t think that that in itself undermines the alliance.”

Correspondent Karla Adam in London contributed to this report.