WASHINGTON -- Defense Secretary Robert Gates says there will be no American ground troops in Libya as long as he's in his job.

Gates made the comment under congressional questioning about the U.S. mission in Libya.

Speaking to the House and Senate Armed Services Committees, Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, described a limited role for the U.S. military. They said as time goes on, the U.S. will play a less active role in airstrikes.

But Gates and Mullen were unable to answer questions from lawmakers about the length of the operation and how it will play out if Moammar Gadhafi doesn't relinquish power.

Some lawmakers complained that Congress hasn't been consulted on the Libya operation, and the goals are unclear.

Gates and Mullen say Gadhafi's military has been degraded by as much as 25 percent, but the opposition groups are fractured and just 1,000 of the rebels have military training.