Muammar Gaddafi vowed to hang on to power in a speech Wednesday--and regime forces are reported to have made territorial gains, raising the prospect of a civil war in Libya. The United States is under increasing pressure to consider forceful action to avert a bloodbath in the country, from imposing a no-fly zone to setting up humanitarian corridors to protect civilians.

But Defense Secretary Bob Gates made clear Tuesday that, with 150,000 U.S. forces already deployed in Afghanistan and Iraq and unrest simmering from Algeria to Yemen, he's reluctant to commit U.S. military forces elsewhere in the Middle East. However, the United States ordered the deployment this week of two Navy vessels, including the amphibious assault ship the Kearsarge, and 400 U.S. Marines toward Libya from the Persian Gulf.

"We also have to think about, frankly, the use of the U.S. military in another country in the Middle East," Gates told reporters at the Pentagon Tuesday.

"If we move additional assets, what are the consequences of that for Afghanistan, for the Persian Gulf?" Gates said. "And what other allies are prepared to work with us in some of these things?"

Top U.S. military brass also warned Congress Tuesday that imposing a NATO no-fly zone over Libya to protect civilians from air attack by Gaddafi's forces would be a far more complex endeavor than many appreciate. It would require first taking out Libya's air defenses.

"So no illusions here," CENTCOM Commander Gen. Jim Mattis told the Senate Armed Services Committee. "It would be a military operation. It wouldn't be just telling people not to fly airplanes."

The latest Middle East crisis poses a key dilemma for the Obama administration, pitting humanitarian concerns against broader Middle East strategic considerations. The involvement of U.S. military forces even in an internationally led operation intended to avert atrocities against Libyan civilians could give a sharp anti-American cast to the anti-government unrest in the Middle East. But even as military advisers urge restraint, some in Congress and key humanitarian and pro-democracy advocates are urging the Obama administration to take more forceful measures to avert possible bloodshed.

Middle East experts note the Obama administration has already taken a number of steps in close consultation with international allies. Among these are the passage of a U.N. Security Council resolution sanctioning Libya on Saturday, the opening of an International Criminal Court investigation of Libyan war crimes, freezing $30 billion in Libyan assets in the United States on Sunday--and the symbolic measure voting Libya off the UN Human Rights Council in Geneva on Monday.

"I think a no-fly zone, targeted sanctions, and referral to [the International Criminal Court] are all realistic and appropriate," said George Washington University Middle East expert Marc Lynch, who has consulted with the White House several times over the past month on both Egypt and Libya. "It's extremely important to send a signal not just to Gaddafi but to all the other dictators in the region and world who might be tempted to use brutal violence against their people to stay in power that it's not actually going to keep them in power."

Experts said at this stage, the movement of U.S. naval power towards Libya was more about messaging than action--persuading Gaddafi loyalists that his downfall is imminent.

"They are sure hoping they don't have to use them and that this thing will be over, everyone keeps hoping, before they have to take more drastic and costly measures," said the Carnegie Endowment for International Peace's Michele Dunne, a former State Department and NSC official who has also been in frequent consultation with the White House.

Former State Department Middle East official Joel Rubin, now with the progressive National Security Network, says the real question for the United States is defining an end goal.

"On the practical level, defining the goal is essential," Rubin said. "If we have learned anything from our recent experience of military adventures in the Arab world, it is that we have to have a clear and compelling goal that is achievable. And in the case of Libya, there are two goals … the first is humanitarian protection, and the second is removing Gaddafi." Rubin said that a no-fly zone is the option that analysts are discussing most frequently on the humanitarian front.

But Rubin said even a no-fly zone will not be a panacea. "At this point, Gaddafi is strong because he has guns and money. By deploying a no fly zone … you attempt to reduce his guns, and by utilizing sanctions and asset freezes, you attempt to take away his money. Once those are both gone, yes he is beatable," Rubin said. "But there's no single magic bullet. There's no shock and awe."