WASHINGTON — NATO will assume leadership from the United States of patrolling the skies over Libya but the military alliance remains divided over who will command aggressive coalition airstrikes on Col. Muammar el-Qaddafi’s ground troops, NATO and American officials said Thursday.

After a day of confusion and conflicting reports out of NATO headquarters in Brussels, Secretary of State Hillary Rodham Clinton announced late Thursday in Washington that NATO had agreed to lead the allies in maintaining the no-fly zone. Effectively, that means that planes from NATO countries will fly missions over Libya with little fear of being shot down since Tomahawk missiles, most of them American, largely destroyed Colonel Qaddafi’s air defenses and air force last weekend.

But NATO and American officials said NATO had balked at assuming responsibility, at least for now, of what military officials call the “no-drive zone,” which would entail bombing Colonel Qaddafi’s ground forces, tanks and artillery that are massing outside crucial Libyan cities, and doing so without inflicting casualties on civilians.