At a morning hearing of the the House Armed Services Committee, Defense Secretary Robert Gates told members that political turbulence in the Middle East and Northern Africa holds “peril and promise” for the U.S.

The same could be said for President Obama’s decision to drop bombs on Libya, a military engagement Gates and Joint Chiefs Chairman Adm. Mike Mullen were on Capitol Hill to defend as crucial to preventing a massacre and causing a destabilizing flow of refugees into Egypt and Tunisia.

It was the first in a series of four congressional hearings today, and the nation’s top military leaders faced tough but largely respectful questions from skeptical members on both sides of the political aisle.

Their answers did little to assuage members deeply concerned about the aims and $550 million-and-rising cost of the mission. Or how the White House arrived at its decision to join in international coalition air strikes against the government of strongman Moammar Gadhafi.

Still, Gates and Mullen provided perhaps the most expansive view yet of how President Obama perceives U.S. military involvement in Libya.

Some highlights:

*The administration considers hard U.S. military action over Thursday - no more U.S. air strikes, Gates said - as control of the mission and maintaining the no-fly zone are handed off to NATO. Regime change, he said, is a political goal, not the objective of the U.S. military mission.

*There is no time frame for how long the U.S. military will be involved in other activities in Libya.

*No decision has yet been made about arming rebels, though, Gates said, and more than once, that there are “other countries” who could arm and train rebels - including those in the Arab world.

*There will be no U.S. military ground troops deployed in Libya, no “boots on the ground,” except for search-and-rescue missions. (The CIA, however, has operatives working now in the country.

The president, Gates said, has no additional military moves in mind beyond what he’s already authorized. Gates also defended the president’s decision to begin air strikes without congressional approval - actions, he said, that were consistent with those taken by every president since the 1973 War Powers Act was approved.

This, Gates said, has been an area of contention between Congress and the executive branch for more than 35 years. Rep. Randy Forbes, a Virginia Republican had another way to describe it - “a shaking down of the rule of law,” he said, where the ends justify the means.

But Gates and Mullen were, perhaps unintentionally, was far less reassuring when pressed to answer questions about just who the U.S. is “aiding and abetting” in Libya, as GOP Rep. Roscoe Bartlett of Maryland phrased it.

They provided a stark and troubling view of the state of the rebel uprising, and the uncertainly of what could happen if Gadhafi is driven out or killed.

The opposition movement, Gates said, is disparate, scattered, with a handful of leaders with their own agenda.

“It’s pretty much a pick-up ballgame,” he said, with no “command and control.”

Gates, later pressed Republican Rep. Todd Young of Indiana about whether the leadership vacuum could be exploited by terrorist groups including al-Qaida or Hezbollah, said it’s “highly unlikely.”

“I’m no great expert on Libya,” he said, but predicted that the future government there, if Gadhafi leaves or is removed, will be worked out among the country’s many and powerful tribes.

Mullen said that some tribal leaders have been seen hedging their bets, waiting to see whether the opposition takes hold.

What rebels still face, even with Gadhafi’s air power largely destroyed wasn’t pretty. A military of up to 20,000, a “significant amount of capability” in tanks and armored personnel carriers - or about a 10-1 advantage over rebels, Mullen said.

He’s got equipment, training and control, Mullen said. Which Rep. Rick Larsen, a Washington Democrat, tried to get at.

How, he asked, does a leaderless opposition organize to defeat Gadhafi?

Best case scenario for the U.S., Gates said, is for tribal leaders and rebels to come together and force regime change.

But nation building? No way, he said.

Tribes? Regime change? Nation building? Armed despotic leaders? Attrition?

For many members, it was felt like deja vu all over again.

Rep. Niki Tsongas, a Massachusetts Democrat, had something of a poignant message for Gates and Mullen: “I don’t think when last you were before us, we imagined you’d be back quite so soon.” Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.