While Congressional leaders have been calling for the Obama administration to intervene in Libya, Pentagon officials have demurred.

“There’s a lot of, frankly, loose talk about some of these military options,” Defense Secretary Robert Gates told the House Appropriations Committee. “Let’s just call a spade a spade. A no-fly zone begins with an attack on Libya to destroy the air defenses. That’s the way you do a no-fly zone.”

Secretary Gates will offer President Obama “a range of options,” but he “believes it is his duty to also present what the possible ramifications are of each option that is being considered,” said Pentagon spokesman Geoff Morrell, with an eye towards NATO meetings Thursday that are likely to be dominated by discussion of the feasibility of a no-fly zone in Libya.

Gates is not the first Pentagon official to emphasize the difficulty of implementing a no-fly zone. But Congress is increasingly challenging whether it is really such a tricky prospect for the most exquisitely-equipped military in the world.

“I would like to point out [Libya's] air assets are not large,” said Sen. John McCain (R) of Arizona, ranking member of the House Armed Services Committee, on ABC’s This Week with Christiane Amanpour. “Their air defenses are somewhat antiquated.”

Defense analysts largely concur. Putting aside the outcome of NATO talks this week and the politics of coalition-building, some options for creating a no-fly zone don’t involve a great deal of risk to US troops, they say. These might include stealth bombers or cruise missiles that could be launched from submarines or aircraft carriers in the Mediterranean, or using Predator and Reaper drones.

“Why did we bother building a stealth bomber” if not to use it to take out Libyan air defenses in the midst of a humanitarian crisis, asks Michael Knights, Lafer fellow in the Military and Security Studies Program at the The Washington Institute for Near East Policy.

“Cruise missiles all would have the range to hit anything in northern Libya – anything that matters there is within 20 kilometers of the coast,” Dr. Knights adds. “This stuff is easy-peasy for the United States. This is not Iraq or Afghanistan ground warfare. This is the kind of stuff the US military excels at.”

What’s more, while the Army and Marine Corps have been heavily engaged in Iraq and Afghanistan, the Navy and Air Force “are not tied down in two conflicts,” Knights says. “We’re doing ourselves a little bit of a disservice by making a no-fly zone seem like it’s harder than it is.”

So why does the Pentagon continue to underscore the risks of such an operation? “A characteristic of the US military is we make the difficult look easy – so people tend to default to the military. ‘Oh, we’ll put up a no-fly zone,’ ” says retired Lt. Gen. David Deptula, the Air Force’s former Deputy Chief of Staff for Intelligence, Surveillance, and Reconnaissance.

There are some important questions that the Obama administration – and by extension, the Defense Department – have yet to determine. “A no-fly zone over what part of the country? Only the region [Libyan leader Muammar] Qaddafi has control over? For what period of time?” Deptula asks.

What’s more, “It would be wise to think about what we want the desired outcome to be,” he adds. “What are the US strategic interests?”

Actually, the US has a number of of strategic interests, says Michael Singh, who was former senior director for Middle East affairs at the National Security Council until 2008. “Certainly energy. Libya is not only a critical supplier, but the current instability has an impact on energy prices throughout the world, and that in turn has an impact on the economic security” of the United States.

The US also has an interest in preventing humanitarian disaster, Mr. Singh says, though critics question why America would intervene in Libya while ignoring mass killings in other African nations.

Secretary of State Hillary Clinton warned about concerns that the US would “invade for oil.”

Gates cautioned against what might be said if the US takes action in “another country in the Middle East.”

Yet just because the US has "ignored” humanitarian crises in other parts of Africa does not mean it should do it now, says Singh. What’s more, the institutional conservatism of the Pentagon should not override US interests, he argues. “Not acting has consequences. You can’t get away from the consequences by not acting.”

For example, Libyan opposition has requested US airstrikes against Colonel Qaddafi and could resent ongoing US non-intervention. The problem, says the Washington Institute’s Knights, is that if a no-fly zone helps Libyan rebels launch an assault on, say, Tripoli, the mission “is not humanitarian any more. The United States effectively becomes a combatant – we are effectively picking a side.”

And US officials still know little about the Libyan rebels. Eastern Libya “has been a strong radical Islamist base since the 70’s. It’s the place that provided one of the largest number of foreign fighters to Al Qaeda in Iraq,” Knights says. Many of the mid-ranking Al Qaeda operatives in Afghanistan and Pakistan are also Libyans, he adds.

Helping the opposition rebels could “earn ourselves significant brownie points” with some conservative Muslims, Knights says. “The lesson might be, we can support these kinds of Islamist movements, but the key is to remain in touch with them and guide their development. The problem,” he adds, “is the gross uncertainty – we just don’t know. That’s part of the reason why Gates is urging caution.”

Indeed, the uncertainty comes with possible rewards. “There are risks with a no-fly zone, and the chance that it could bring the conflict to an earlier close,” says Singh.

“This is why military decisions are hard," he adds. "If they came with a guarantee of military victory, there would be no question about what to do.”