BRUSSELS – NATO agreed late Thursday to take over part of the military operations against Libya — enforcement of the no-fly zone — after days of hard bargaining among its members.

But the toughest and most controversial portion of the operation — attacks on the ground — will continue to be led by the US, which has been anxious to give up the lead role.

NATO Secretary-General Anders Fogh Rasmussen, who announced the agreement in Brussels, said the alliance could eventually take more responsibility, "but that decision has not been reached yet."

It appeared that some NATO members balked at any involvement in attacks on ground targets, something the alliance's sole Muslim member, Turkey, has resisted.

In Washington, Secretary of State Hillary Rodham Clinton praised NATO for taking over the no-fly zone, even though the US had hoped the alliance would take full control of the military operation.

The operation cost the US close to $1 billion in less than a week, and has drawn criticism in Congress from members of both parties.

NATO said that it expected to commence enforcement of the no-fly zone within two to three days. The operation will be commanded from Naples by Adm. Samuel J. Locklear.

NATO also agreed to launch military planning for a broader mandate, including a "no-drive" zone that would prevent Libyan leader Moammar Gadhafi's armor and artillery from moving against rebels. The North Atlantic Council is scheduled to meet on Sunday to consider the broader plans.

Diplomats also have drawn up plans to put political supervision of NATO's effort in the hands of a broader international coalition. US, European, and Arab and African officials have been invited to London next week to work out the details.

"The political coordination cannot be only NATO because there are countries there that are not members of NATO," Sarkozy said.

US weapons are being used less frequently than they were when airstrikes began. French fighter jets used deep inside Libya on Thursday hit aircraft and a crossroads military base.

"Nearly all, some 75 percent of the combat air patrol missions in support of the no-fly zone, are now being executed by our coalition partners," US Navy Vice Adm. William Gortney, told reporters Thursday at the Pentagon. Other countries were handling less than 10 percent of such missions Sunday, he said.

The US will continue to fly combat missions as needed, but its role will mainly be in support missions such as refueling allied planes and providing aerial surveillance of Libya, Gortney said.

Allies have especially sought military assistance from Arab countries, seeking to avoid an all-Western military presence. Qatar is expected to begin flying air patrols this weekend, and on Thursday Clinton praised a second Arab nation, the United Arab Emirates, after it agreed to deploy 12 planes.

NATO's top decision-making body, the North Atlantic Council, had been struggling for six days to reach an agreement on using its military command and control capability to coordinate the operation in Libya.

Senior Obama administration officials said the breakthrough came in a four-way telephone call with Clinton and the foreign ministers of Britain, France and Turkey.

The four worked out the way forward, which included the immediate transfer of command and control of the no-fly zone over Libya, and by early next week of the rest of the UN-mandated mission.

The officials, speaking on condition of anonymity to discuss sensitive military planning, said the actual handover of the no-fly zone would occur in one or two days.

Turkey's parliament on Thursday authorized the government to participate in military operations in Libya, including the no-fly zone.