With the imposition of sanctions on the regime of Muammar Qaddafi producing no discernible sign that the Libyan dictator will follow the demands of Western leaders and swiftly resign – indeed, he laughed at the notion, when confronted by a TV interviewer on Monday – top U.S. officials are preparing for the possibility that the Libyan conflict will drag on much longer than the real-time revolution that toppled Hosni Mubarak from power in Egypt.

“Sometimes you actually have to listen to what people say, and he's saying he's not leaving,” Defense Secretary Robert Gates said of Qaddafi during a session with reporters at the Pentagon on Tuesday.

“Libya could become a peaceful democracy, or it could face protracted civil war or it could descend into chaos,” warned Secretary of State Hillary Clinton, in testimony before Congress.

Likewise, White House Press Secretary Jay Carney cautioned reporters not to expect immediate results from the sanctions, which were imposed in a concerted fashion both unilaterally by the United States and by international organizations like the United Nations Security Council and the European Union.

“I understand that as we all watch the events in the Middle East, in Libya and other countries, that the drama we are witnessing creates in us a sense of urgency,” Carney said, adding: “I just think you cannot reasonably measure momentum in this situation in terms of hours and days.”

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A senior administration official, who requested anonymity so he could speak freely about affairs of state, acknowledged that the first round of Western action in response to the regime’s crackdown had failed to dislodge Qaddafi from his defiant stance. “His posture is he’s digging in,” the official said. “We are planning for both short-term and long-term contingencies.”

Further evidence that the Obama administration is prepared for a more protracted engagement with the Libyan crisis came from U.N. Ambassador Susan Rice, who told ABC News: “We are going to keep the pressure on Qaddafi until he steps down.”

While President Obama and Clinton began calling on Qaddafi to resign this past weekend, Rice’s statement marked the first time a senior U.S. official had gone beyond merely advising a course of action for the Libyan leader, and instead identified his departure as the strategic objective of U.S. policy.

In separate appearances before lawmakers on Capitol Hill on Tuesday, Clinton and the top American military commander in the Mideast each conveyed the impression that the U.S. is not rushing to establish a no-fly zone over Libya, which some human rights activists and others have advocated as a way of preventing the Qaddafi regime from carrying out further aerial attacks on Libyan rebels.

“We are also very conscious of the desire by the Libyan opposition forces that they be seen as doing this by themselves…that there not be outside intervention by any external force, because they want this to have been their accomplishment,” Clinton told the House Foreign Affairs Committee. “We respect that.”

When Rep. Steve Chabot, R-Ohio, challenged Clinton, calling the Obama administration’s initial response to the crisis “tepid,” the secretary shot back: “We feel that we did this in a prudent and effective manner, and we did it in a way that did not raise the alarm bells around the region and the world that we were about to invade for oil. If you follow, as we follow, all of the websites that are looking at what's happening in the Middle East, you see a constant drumbeat that the United States is going to invade Libya to take over the oil….Well, we are not going to do that. And we are going to side with the Libyan people and their aspirations. But the last thing in the world we wanted was to start off with military assets when we very effectively got our people out [of Tripoli].”

Gen. James Mattis, commander of U.S. Central Command, told a Senate panel the establishment of a no-fly zone over Libya would effectively protect Libyan protesters and rebels from aerial attacks by the regime. But Mattis also warned lawmakers not have any “illusions” about such an operation, because creating the zone would first require U.S. fighter jets to target and destroy Libyan air defenses.

“It would be a military operation,” the general said. “It wouldn't be just telling people not to fly airplanes."