As international forces launched attacks against Libya on Saturday, Secretary of State Hillary Rodham Clinton struck a tone highly unusual in the annals of American military interventions: humility.

“We did not lead this,” she told reporters.

But her modest words belied the far larger role the United States played as international forces began an open-ended assault on Libyan leader Moammar Gaddafi’s military capabilities. U.S. warships fired more than 110 Tomahawk missiles into Libyan territory to disable air-defense systems. And the French and British warplanes that began to enforce the emerging no-fly zone operate under U.S. command.

Vice Adm. Bill Gortney, director of the Joint Staff, described the U.S. role to reporters at the Pentagon: “We are on the leading edge of a coalition military operation.”

The administration’s mixed message reflects the challenge President Obama faces at home and abroad as he opens a third military front in a Muslim nation.

Obama has spent much of his first term seeking to repair U.S. relations with the Islamic world, and his emphasis on the international support for military strikes in Libya is an attempt to allay suspicions over U.S. intentions. And as budget deficits mount at home, the American public is looking for other nations to carry the fiscal burden of the fighting after a nearly a decade of war.

But U.S. diplomats were key in broadening and securing a United Nations resolution authorizing military force in Libya, and U.S. military power proved essential Saturday in preparing the battlefield for a no-fly zone to be enforced by European and possibly Arab nations.

As much as Obama has sought to strengthen the international organizations that the previous administration disdained, the United States remains essential to the operation in Libya, despite the president’s and Clinton’s efforts to play down the American role.

The early cooperation may be tested soon as signs emerge that the Obama administration and its European allies, particularly French President Nicolas Sarkozy, differ over how long military operations will last and to what end.

Sarkozy has spoken out far more aggressively than Obama on the danger Gaddafi poses to his people and the region, suggesting an endgame that includes his removal from power. But U.S. officials stressed Saturday that the resolution and the operations underway now are focused on protecting Libyan civilians from Gaddafi’s advancing forces, not pushing him from power.

Mark Quarterman, a senior adviser at the Center for Strategic and International Studies in Washington, said the risk in Libya is that the military operation will not end quickly or decisively. He said it is easy to imagine Gaddafi’s well-armed government remaining strong, despite the no-fly zone.

“After the first few days, this could settle into a protracted fight between Gaddafi and the rebels, essentially a stalemate with neither side able to retake ground or negotiate an end to the fighting,” he said. “Then what do you do?”

Both Obama and Clinton have emphasized that no U.S. ground troops will be involved in the Libya operation. Ben Rhodes, the deputy national security adviser for strategic communications, told reporters that “the contribution from the United States will be at this front end” — such as the missile attacks to clear the way for French and other nations’ warplanes.

“And the enforcement of the no-fly zone over time will be up to our allies and partners,” said Rhodes, who was traveling with Obama in Brazil.

The administration’s approach had been criticized across a broad political spectrum of U.S. lawmakers and activists, who see a lack of leadership in Obama’s part-of-a-team approach.

But David Mack, a ­former senior U.S. diplomat in the Middle East, said Obama is aware of the dangers of another clash with Libya that Gaddafi could cast as unilateral American intervention. Mack cited the 1986 bombing raid of a Gaddafi compound authorized by then-President Reagan, who dubbed the Libyan leader “the mad dog of the Middle East.”

“The rhetoric was very satisfying,” Mack said. But despite the bombing, unilateral financial sanctions, and covert arming of Libyan rebels, he said, “we didn’t change his behavior one whit.”

The U.S. government is more unpopular in the Muslim world than it was in the 1980s, after a decade of war in Afghanistan and Iraq, which the United States invaded in 2003 without U.N. support.

On Saturday, Clinton emphasized the role that Middle Eastern countries are playing in the operation, saying that the recent Arab League endorsement of no-fly zone over a member country “changed the diplomatic landscape.” At least three Arab countries have promised to contribute to the military operation, U.S. officials said.

As the military operation began, Sarkozy appeared to take a more central role than Obama. He made the first announcement that the military operations had begun, declaring to a large audience gathered for the summit that French warplanes had been dispatched to Libya. Clinton, by contrast, spoke only to the handful of American reporters traveling with her.

The muted diplomacy and message is a way to play down the conflict to the American public as well. A Pew Research Center survey released last week found that more than six in 10 Americans do not believe the United States has a responsibility to do something to stop the conflict in Libya.

Beyond public opinion, the Pentagon is also wary about the resources that a prolonged military operation in Libya will require and whether its current goal of protecting civilians will expand to include Gaddafi’s removal. Obama has said the Libyan leader “must leave.”

But for now, the U.S. military is in charge of the intervention in Libya.

International military forces are operating under the command of Gen. Carter F. Ham, head of the U.S. African Command. The Pentagon says command will be turned over to the coalition in coming days, although which country will lead it remains unclear.

Wilson reported from Washington.