Several members of Congress have said Obama should have consulted with Congress before committing to action in Libya, including Rep. Ron Paul (R-Texas), who spoke about this on the House floor last week, as well as Reps. Mike Pence (R-Ind.) and Charles Rangel (D-N.Y.) this week. Van Hollen explained that under the War Powers Resolution, Obama has the flexibility to commit troops for 60 days, with the possibility of a 30-day extension. Extending troop commitments beyond that would require a congressional authorization of military forces or a declaration of war.

But Van Hollen said he does not believe troops will continue to operate in Libya for that long.

"Based on what the president has said the rationale for this action is, I expect it to be, as he has said, a matter of days, not weeks," Van Hollen said. "We are going to be transitioning the command and control operations very quickly to either NATO or some other international group."

However, speaking from Brazil on Monday, Obama indicated that U.S. military forces may be involved in enforcing a no-fly zone in Libya for longer than just a few days or weeks. In a press conference, Obama said that once Col. Moammar Gadhafi's air defenses are disabled, "there is going to be a transition taking place in which we have a range of coalition partners — the Europeans, members of the Arab League — who will then be participating in establishing a no-fly zone there."

Obama added that there would be a transition "in which we are one of the partners among many who are going to ensure that the no-fly zone is enforced and that the humanitarian protection that needs to be provided continues to be in place." But he did not say how long that would last.

For now, Obama stressed that the U.S. is focused on the narrow mission of preventing Gadhafi from killing Libyan citizens. "When it comes to our military action, we are doing so in support of U.N. Security Resolution 1973, that specifically talks about humanitarian efforts," Obama said. "And we are going to make sure that we stick to that mandate."

Obama on Monday sent a letter to Congress outlining his authority under the War Powers Resolution to commit forces in Libya for a limited duration.