"No, no -- it was not a vital national interest to the United States, but … the engagement of the Arabs, the engagement of the Europeans, the general humanitarian question, that was at stake," Gates said.
"For all practical purposes, the implementation of a no-fly zone is complete. Now it will need to be sustained, but it can be sustained with a lot less effort than what it took to set it up," Gates said.
Appearing alongside Gates on "This Week," Secretary of State Hillary Clinton defended the mission in Libya while downplaying its length.
"I think that this had a limited timeframe, a very clearly defined mission, which we are in the process of fulfilling," Clinton said.
ABC News' Kirit Radia contributed to this report