Panetta later had his first discussions at NATO headquarters since taking over the top Pentagon job over the summer. His message echoed the blunt parting words of his predecessor, Robert M. Gates: One nation can't do it all.
"It would be a tragic outcome if the alliance shed the very capabilities that allowed it to successfully conduct these operations," Panetta said.
His comments came as NATO chief Anders Fogh Rasmussen left the door open for an extended mission in Libya, saying the civilian population must be protected until "no threat exists."
The NATO secretary-general acknowledged that the Libya mission showed NATO lacking in a number of critical capabilities, including surveillance drones and air refueling, and had to rely on the United States to fill the gaps. "If we are to respond to the challenges of tomorrow just as effectively, more allies should make sure they obtain and maintain those kinds of critical capabilities," Fogh Rasmussen said. "One is not enough."
His remarks mirrored the key points in Panetta's speech. The allies, said Panetta, must work better together and pool their resources or risk losing the ability to take on big missions.
It is too soon to say whether the criticism will have much impact on European nations who are also facing fiscal crises and, in many cases, see little benefit to getting more involved in these wars.
But Panetta continued the U.S. drumbeat for more NATO contributions, and he made it clear that with the Pentagon facing $450 billion in budget cuts over the next 10 years, allies can't assume the United States will be able to do what NATO can't or won't on its own.
Just three months into the job, Panetta tried to soften the edges of the blistering critique Gates delivered in June, while identifying many of the same frustrations. Gates had questioned the alliance's very viability and bluntly warned that it faces a "dim, if not dismal, future."
"We cannot afford for countries to make decisions about force structure and force reductions in a vacuum, leaving neighbors and allies in the dark," Panetta said, adding that the missions in Libya and Afghanistan have highlighted serious shortfalls in the alliance.
In Libya, he said, there has been a shortage of intelligence and surveillance capabilities, including drones and experts who can interpret data and translate it into targeting lists. The United States has had to shift drones from other critical regions to meet the needs of the Libya mission.
In addition, he pointed to shortages of ammunition and supplies as well as refueling tankers - all gaps the United States had to fill.
"We are at a critical moment for our defense partnership," Panetta warned.
"I am convinced that we do not have to choose between fiscal security and national security," he said. "But achieving that goal will test the very future of leadership throughout NATO."