By THOM SHANKER and STEVEN ERLANGER - BRUSSELS — Defense Secretary Robert M. Gates sharply criticized NATO nations on Friday for what he said were shortages of military spending and political will, warning of “a dim if not dismal future” and “irrelevance” for the alliance unless more member nations contributed weapons, money and personnel.
In his final policy speech before he steps down, Mr. Gates issued a dire and unusually direct warning that the United States, the traditional leader and patron of the alliance, was exhausted by a decade of war and its own mounting budget deficits and simply might not see NATO as worth supporting any longer.
“The blunt reality,” Mr. Gates said, “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.”
The White House made clear on Friday that in the tough tone of his remarks, Mr. Gates was speaking for the Pentagon, not necessarily for the administration, and that he appeared to be expressing his own frustrations after years of asking NATO to do more. But a White House official did say that Mr. Gates’s speech raised “legitimate concerns” about whether NATO was providing enough resources for the war and that the Obama administration fully expected the alliance to meet its challenges.
The United States accounts for about three-quarters of total military spending by all NATO countries, and it has in the past taken the lead in military operations and provided the bulk of the weapons and matériel. But in a post-Soviet world, there is growing resentment in Washington about NATO effectively paying for the defense of wealthy European nations.
Those strains have deepened considerably during the air war against Libya’s leader, Col. Muammar el-Qaddafi, the first NATO-run multilateral war where Washington has pulled back from a leadership role.
The strains come from varying commitments to the war from different NATO countries, the difficulties of coordinating air attacks, deficiencies of aircraft and ammunition and the simple cost of the operation, which is going on longer than many countries, including France, expected when it began on March 19.
Although NATO ambassadors attended Mr. Gates’s speech, the reaction was muted, and there was little response from NATO capitals, which have heard similar criticisms from Mr. Gates before, though not in such candid terms. “But people should take note,” one NATO ambassador said. “This is not just an old curmudgeon leaving office. He cares about the alliance and says you need to start investing in it.”
NATO’s shortcomings have long been the subject of black humor in Afghanistan, where American military officers sometimes refer to the official NATO command — called the International Security Assistance Force, or ISAF — as “I Saw Americans Fighting.” In recent months, the aggravation with NATO in Afghanistan has intensified because of Libya.
“The Europeans enjoy generous social welfare programs in part because the United States subsidizes their defense spending,” said Andrew M. Exum of the Center for a New American Security, a military research organization, who was an Army infantry officer in Afghanistan in 2002 and 2004.
If the United States did not have large stockpiles of ammunition, a senior NATO official said, the NATO campaign would already have come to a halt. The Americans are selling the ammunition, but it was the American military budget that paid for its manufacture and stockpiling.
Similarly, NATO allies must still rely on American Awacs planes and refueling aircraft, American suppression of air defenses and American intelligence gathering. Even with the United States playing a secondary role, by mid-May its operations in Libya had already cost $664 million, according to a Pentagon memo circulating in Washington, The Financial Times reported. To a certain extent, the Libyan campaign represents precisely the shift that Mr. Gates warned was coming — namely, the European nations paying for more of their own security, and to that extent it represents a “major strategic shift,” said François Heisbourg, a defense expert at the Foundation for Strategic Research.
But the Libyan campaign has also revealed inadequacies in European budgets and equipment that are likely to have a bigger impact on European spending than any swan-song scolding from an American official, no matter how respected.
At about $2 million a day, by some estimates, France is spending almost as much on Libya as it is on Afghanistan, French officials said Friday, and about the same as the United States is currently spending per day.
Even at a lower estimate of roughly 1 million euros a day — about $1.45 million — Libya has already cost France at least $120 million. But the costs are likely to have increased since the United States pulled back from a leadership position.
The French budget for military operations abroad is about $900 million for 2011, said René Carlé, the defense expert for the finance committee of the National Assembly. But the budget is “always underestimated,” and the government typically comes back to Parliament for supplementary financing. In 2008, the final operations budget was $1.2 billion, he said.
Last year, he said, French operations in Afghanistan, where there are ground troops, cost about $675 million. Adding that to the Libya operation will badly stretch the budget, and then there will be more costs to restock.
Britain, too, is being cagey about its spending in Libya, even as the current government vows to cut military outlays by about 8 percent over the next four years. There are estimates that Britain is spending about the same amount as France, around $9.8 million a week. But the British defense secretary, Liam Fox, has said that the budget is adequate for both Libya and Afghanistan.
Britain and France rank second and third within NATO on defense spending, after the United States. But Britain’s military budget is only about 7.7 percent of Washington’s. (France’s is about 6.6 percent.) Norway and Denmark have tiny military budgets of only $6.4 billon and $4.5 billion respectively, yet they have been flying strike missions over Libya, while much larger countries like Germany and Spain have not — but not because they lack the capacity, but because they disagree politically with the airstrikes.
Europeans argue that they are spending blood and treasure to support Washington in Afghanistan against the Taliban and Al Qaeda, far from Europe, and they are eager to draw down their forces there. NATO, some argue, would be best served, since Russia is no longer judged to be an adversary, as an alliance with more limited goals like defending Europe against other kinds of threats, like piracy, cyberattacks or natural disasters.
But Mr. Gates is not alone in arguing that the European allies must spend more to keep credibility with the United States.
In February, even before Libya campaign, NATO’s secretary general, Anders Fogh Rasmussen, delivered a similarly strong warning about shrinking military expenditures to Europeans at a security conference.

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Thom Shanker reported from Brussels, and Steven Erlanger from Paris. Stephen Castle contributed reporting from Brussels, Elisabeth Bumiller from Washington, and Romain Parlier from Paris.