The U.S. military was pulling its warplanes from front-line missions Monday and shifting to a support role in the Libyan conflict, officials said.
Britain, France and other NATO allies will now provide the fighter jets for intercept and ground-attack missions that enforce a no-fly zone over this North African country.
The hand-over is expected to take place later Monday, a NATO official said.
"There won't be a capabilities gap," said the official, who spoke on condition of anonymity because of regulations.
Another official, who could not be named for the same reason, said the U.S, would continue to play a major role in the operation, with one of the largest national contingents. Most U.S. planes will perform switch to support tasks, leaving offensive tasks to their NATO allies.
In Washington, Defense Department spokesman Navy Capt. Darryn James said U.S. activity will formally end at 2200 GMT (6 p.m EDT.)
U.S. aircraft currently account for 90 of the 206 planes deployed by NATO in the Libyan conflict.
Secretary of Defense Robert Gates told Congress last week the U.S. would continue to provide assets that others don't have in sufficient numbers. These will likely include AWACS air surveillance planes, electronic reconnaissance aircraft and aerial refueling tankers.
American air power _ including Air Force AC-130 gunships and A-10 Thunderbolts and Marine Corps AV-8B Harriers _ will still be available to back up the allies in case of need.
Western jets have been hitting the forces of Libyan leader Moammar Gadhafi for more than two weeks. They initially targeted anti-aircraft missile defenses and quickly crushed a government offensive by destroying a large number of tanks, armored vehicles, artillery and other vehicles advancing into rebel-held areas.
But military experts say Gadhafi's forces have rapidly reorganized since then, shedding their heavy armor and relying on light forces to harry and repeatedly ambush the lightly armed rebels.
NATO said its aircraft flew 154 sorties over Libya on Sunday, the fourth day since the alliance assumed full control over the mission from the U.S.-led international force. It described 58 of those flights as "strike sorties."
NATO does not release information on the number of targets bombed.
In the first four days of the NATO operation, alliance aircraft have flown a total of 701 sorties, the statement said.
Flights by fighters and attack jets accounted for 40 percent of that total. The rest are by AWACS surveillance aircraft, aerial refueling tankers, maritime patrol planes, search and rescue helicopters and other support aircraft.
Associated Press writer Pauline Jelinek in Washington contributed to this report.