Briefing reporters in Rio de Janeiro, Donilon said that based on information from members of the Libyan National Council, coalition air strikes against Libyan government targets have prevented a "catastrophe."
He said the threat to the rebel-held city of Benghazi was a main impetus behind the approval last week of U.N. Security Resolution 19-73 that approved military action in Libya.
"This has been confirmed to us from conversations that we have had from various people in Benghazi, including former representatives from the Libyan National Council, who have been in touch with our representatives and our liaison with them, indicating that in fact the efforts here have made a real difference with regard to the threat that was looming over Benghazi," he said.
Donilon said the U.N. resolution contains important provisions for a longer-term effort to "present Mr. Gadhafi with choices and isolate and squeeze him over time."
Donilon said the next phase of moving from protecting civilians and enforcing the no-fly zone to transitioning from U.S. coordination to coalition oversight should come within days.
The United States and its partners have stressed that their mandate does not include going after Mr. Gadhafi, although U.S. military Joint Staff Director Admiral William Gortney told reporters Sunday that allied forces would not know whether the Libyan leader is at a defense site they are targeting.
Deputy National Security Adviser for Strategic Communications, Ben Rhodes, said there is no coalition objective for regime change, although Mr. Gadhafi will be subject to longer-term pressures. "There is not a U.N. Security Council resolution mandating regime change in Libya that we're acting to enforce. We're acting to enforce a resolution that has the immediate goal of protecting civilians," he said.
U.S. military Joint Chiefs of Staff Chairman Michael Mullen said on Sunday that it was possible that military operations in Libya will end up with Moammar Gadhafi still in control of part of the country.
National Security Adviser Donilon told reporters that it will be up to the Libyan people to determine Mr. Gadhafi's fate as he faces increasing pressure and "will have to make some choices."
President Obama's only remarks on Libya came during the speech he delivered in Rio de Janeiro on Sunday, in which he spoke of the struggle of people in the Middle East and North Africa for universal rights. "We’ve seen the people of Libya take a courageous stand against a regime determined to brutalize its own citizens. Across the region, we’ve seen young people rise up - a new generation demanding the right to determine their own future," he said.
Mr. Obama repeated what he has said since the beginning of the unrest across the Middle East and North Africa, saying that change must be driven by the people of the countries concerned.
