Updated

As the Obama administration begins to take heat domestically for the rising costs of U.S. involvement in the Libyan war, Defense Secretary Robert Gates hammered European allies for not contributing their fair share in his farewell speech to NATO.

With just 20 days left in office, Gates lashed out, speaking directly to partner nations in Brussels, accusing European allies of dumping the majority of their military burdens onto the laps of the United States. He warned NATO that it risks becoming a relic the United States can no longer afford.

"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," Gates said.

He pointed to Libya as a prime example.

"While every alliance member voted for the Libya mission, less than half have participated at all, and fewer than a third have been willing to participate in the strike mission. Frankly, many of those allies sitting on the sidelines do so not because they do not want to participate, but simply because they cannot. The military capabilities simply aren't there."

The United States pays more than 75 percent of the defense budget for the 28 members of the North Atlantic Treaty Organization. Gates said that by slashing their own defense budgets, the European nations are falling short in Libya.

"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 said.

Gates also took time to credit Norway, Denmark, Canada and Belgium -- countries he said made disproportionately high military contributions. He also paused to acknowledge the 850 non-U.S. NATO servicemembers who lost their lives fighting in Afghanistan.

Knowing he's only on the job for three more weeks, he left American allies with a sense that future American political leaders could be less nostalgic about NATO's post World War II significance.

Meanwhile, as the mission in Libya wears on, the cost is going up.

Defense officials told Fox News that U.S. combat operations in Libya will far exceed the projected cost of $750 million through September 2011 that Gates announced last month. Officials say that by mid-May the U.S. taxpayer had already spent $664 million and there is concern operations could cost more than $40 million for each additional month.

Even if the rate stays at $40 million, and assuming the war lasts through September, the bill will reach at least $844 million. It's a tough pill to swallow for Congress -- already reeling over deficit spending and the fact that the president doesn’t have formal congressional approval to be operating in Libya.

On June 1, NATO announced it will extend the Libya mission for another 90 days beyond the previous June 27 deadline. NATO and Pentagon officials have acknowledged the mission could go longer than that -- however long it takes to complete the mission of protecting civilians.

In his confirmation hearing to be the next secretary of Defense on Thursday, CIA Director Leon Panetta told the Senate Foreign Relations Committee that leaving Col. Muammar al-Qaddafi in power would send a message to our enemies in the region "that our word isn't worth very much if we're not willing to stick to it."