And while the goal of the coalition mission is to not remove Gadhafi from power, Gates said that would be the ideal outcome and that the administration had considered the possibility "of this being a stalemate and a drawn-out affair.
"Unless there's some king of significant change in behavior in terms of his own people, it's hard for me to imagine circumstances in which we would be content to tolerate a government that would have Gadhafi at its helm," he said.
Rep. Walter Jones, R-N.C., expressed frustration at the absence of a defined endgame.
"I get so upset when I hear ... we can't tell you when it's going to end," Jones said. "Gadhafi is absolutely evil, and yet we take the lead on everything. I don't' know where the other countries are. Why in the world don't they take the lead on something?"
President Obama signed a secret presidential finding authorizing covert operations to "aid the effort" in Libya, a source told ABC News Wednesday. While it doesn't direct covert operatives to provide arms to the rebels immediately, it does prepare for such a contingency and other contingencies should the president decide to go down that road in the future.
Gates would not comment on reported CIA activities inside Libya but reiterated that there will be no American boots on the ground.
"Not as long as I'm in this job," he told lawmakers.
Gates said he's not aware of other coalition partners planning to send ground forces.
In the past 24 hours, the United States, NATO and coalition aircraft have flown about 204 sorties, 110 of which were strike-related, hitting fixed and mobile targets in the vicinity of Tripoli, Misurata and Ajdabiyah, Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said today.
He said most of Gadhafi's capability is ground capability, and that the vast majority of his defenses -- at least 20 to 25 percent -- had been destroyed since the coalition began imposing the no-fly zone.
Mullen said the NATO commander, Canadian Lt. Gen. Charles Bouchard, has at his disposal more than 220 aircraft of every size and capability.
Bouchard has said NATO also has 12 ships ready to enforce the naval arms embargo. The organization has conducted 90 flights and sorties since taking over full control earlier this morning.
He also confirmed that NATO is investigating early reports of an air strike in Libya that may have caused 40 civilian casualties.
ABC News' Luis Martinez, Jake Tapper, Martha Raddatz and Alexander Marquardt contributed to this report.