NATO jets on Sunday already began enforcing the no-fly zone, Secretary-General Anders Fogh Rasmussen announced. Diplomats said the full transfer of authority would take several days.
"NATO allies have decided to take on the whole military operation in Libya under the U.N. Security Council resolution," Fogh Rasmussen said in a statement. "NATO will implement all aspects of the U.N. resolution. Nothing more, nothing less."
The North Atlantic Council - the alliance's top body - took two hours to approve a plan to expand a previously agreed mission to enforce the U.N. arms embargo and no-fly zone. It agreed to protect civilians from attack - which effectively means bombing Gadhafi's forces if they are threatening to harm the civilian population.
The U.N. authorized the operation after Gadhafi launched attacks against anti-government protesters who demanded that he step down after 42 years in power.
"In the past week, we have put together a complete package of operations in support of the U.N. resolution by sea and by air," Fogh Rasmussen said.
After eight days of strikes on Libyan targets, Washington is eager to quickly hand off responsibility for the air offensive to the alliance. President Barack Obama and U.S. Defense Secretary Robert Gates have both said that American command of the military operations in Libya would last only a few days.
Gates has said that major strides are being made in bolstering rebels, but acknowledged the international operation could drag on for months. NATO officials said the alliance's operations, approved for up to three months, could be extended if necessary.
A diplomat who asked not to be identified because he was not authorized to speak to the media, said the transfer of authority from the U.S.-led force may take several days. He said the rules of engagement for the NATO force would be very similar to those of the international air armada.
The air strikes have already tipped the balance away from Gadhafi's regular military to the lightly armed rebels, although the two sides remain at stalemate in key cities.
A Canadian three-star general, Charles Bouchard, will be in charge of all NATO operations. He will report to an American admiral, Samuel Locklear, commander of NATO's Allied Joint Force Command Naples.
In a statement released in Naples after NATO took over enforcement of the no-fly zone, Bouchard said the alliance "will do everything it can to deny any use of air power and it will do so with care and precision to avoid harming the people of Libya."
Naples is one of NATO's two operational headquarters. The other, Brunssum in the Netherlands, is responsible for the war in Afghanistan.
The Naples center will coordinate the radar surveillance planes, aerial refueling tankers, maritime patrol aircraft and helicopters needed to maintain the operation 24 hours a day,
NATO has significant experience in such operations. Its warplanes successfully enforced a no-fly zone over Bosnia in the early 1990s and bombed Serbian forces in Kosovo in 1999 in an effort to end crackdowns on ethnic Albanian civilians.