WASHINGTON (CNN) -- While the United States draws closer to providing some form of lethal assistance to the Syrian opposition, the debate over how extensive the package should be and the possible outcome are likely to follow any decision.

In a letter to the Chairman of the Senate Armed Services Committee this week, Joint Chiefs Chairman Martin Dempsey laid out the scenarios that could unfold, ranging from the establishment of a no-fly zone over Syria, to training and assisting the opposition through intelligence and logistics assistance.

None of the options, he said, would be easy, and all would come with a pretty extensive price tag.

"We must anticipate and be prepared for the unintended consequences of our action," Dempsey wrote in the letter to Sen. Carl Levin (D-MI).

"Should the regime's institutions collapse in the absence of a viable opposition, we could inadvertently empower extremists or unleash the very chemical weapons we seek to control."

Some advocates such as Arizona Republican Sen. John McCain say a no-fly zone over Syria is the most effective way to stop the killing machine of President Bashar al-Assad.

"I know that we have the military capability to impose a 'no-fly' zone, to crater their runways and their fixed installations where fuel and parts are, and establish a 'no-fly' zone with Patriot missiles," McCain said in June. "And if we can't do that, then the question ought to be asked to the American taxpayer, to the Pentagon, 'What in the world are we wasting tens of billions of dollars for defense for if we can't even take care of this situation?'"

Pentagon's complex contingencies

But despite costs of such an operation possibly going as high as a "billion dollars per month over the course of a year" as Dempsey wrote in his letter to Levin, analysts say such an option faces other challenges.

Despite the risk to U.S. aircraft and recovery force personnel that may be associated with it, the military involvement in Afghanistan will not end until the end of next year. The Pentagon is also dealing with some complex contingencies in the context of Iran if diplomacy over Tehran's disputed nuclear program fails, as well as other volatile areas in the Middle East.

'Trading modernization against readiness'

The debate also comes at a time when forced budget cuts known as sequestration are shaving billions from the defense budget and forcing some military commanders to question whether the readiness capacity in fiscal environment can handle a new contingency.

"We are trading modernization against readiness, it's the only place we have to go for funding because of this arbitrary mechanism that is sequestration, and it's causing a real problem on the readiness side of the house and putting our ability to modernize over time at risk," Gen. Mark Welsh, chief of staff of the U.S. Air Force, said last week at a security forum sponsored by the Aspen Institute.

Too little too late?

Some of the criticism over the administration's decision to send some form of lethal aid to the Syrian opposition, in a conflict that has claimed nearly 90,000 lives, and more than two years after the conflict began amounts to little more than too little too late.

"Right now, we're playing for the best worst option," Rep. Mike Rogers (R-MI), chairman of the House Intelligence Committee, told CNN's Wolf Blitzer in an interview on the 'Situation Room' Tuesday.

'No guarantees in this business'

Frederic Hof, a former top State Department adviser on Syria, says it would have been better had President Barack Obama endorsed recommendations of former Secretary of State Hillary Clinton, former Secretary of Defense Leon Panetta, and former CIA Director David Petraeus to arm mainstream opposition elements when they recommended it a year ago.

But acting and arming now is better than staying on the sidelines, Hof says.

"There are no guarantees in this business, but when you consider the costs of inaction, of trying to stand aside and watching this problem fester, it's clear to me that just trying to hold Syria at arm's length is every bit as risky as the alternatives, says Hof, now senior fellow at the Atlantic Council's Rafik Hariri Center for the Middle East. "There are no good answers here, no silver bullets."

For Hof, the limited use of "targeted strikes" against specific elements in al-Assad's arsenal responsible for much of the killing, like artillery and missile strikes that reach heavily populated areas, would be an effective tool alongside the provision of small arms and training to the opposition.

"It kind of restricts the amount of expense and the amount of time because you will know with some degree of specificity when you have actually accomplished the mission," Hof says.

Billions of dollars

In his letter to Levin, Dempsey said the cost of such missions could reach billions of dollars, depending on the duration of the operations.

And then what about the disparate state of the Syrian opposition?

Much of the trepidation for greater involvement in the Syrian civil war was the presence of al Qaeda affiliated fighters within opposition ranks, and the danger of weapons falling into their hands.

"There is sort of an idea out there that all of the opposition are extremists," says longtime Syria watcher Andrew Tabler with the Washington Institute for Near East Policy. "They are not, but there are extremists among their ranks."

Who gets the weapons?

For Hof, the funneling of all weapons through Brig. Gen. Salim Idris, the supreme commander of the Syrian Military Council, whom the United States and the West see as an interlocutor, would be an effective organizing mechanism for the opposition.

"Up until now, things have come in with a variety of motives in mind -- different countries and kingdoms wanting clients inside Syria, and private contributors mostly from the [Persian] Gulf wanting to support jihadists," Hof says in advocating for a central figure to funnel everything through. "This is a big reason why there is chaos and disunity in the opposition ranks."

Diplomatic solution still an option

That said, the United States is still pursuing a diplomatic solution through which a political transition would be brokered by all sides of the conflict as long as al-Assad had no role in any incoming government.

While the makeup of any transition government would not include anyone with blood on their hands, as called for by the Geneva Communique signed on to by the United States and other countries, the possible presence of some remnants of the al-Assad regime in a transition government causes pause for some analysts.

"I don't think it will be pulled off anytime soon," said Tabler, who says a process that allows the possible inclusion of regime elements in a new government over a population that has changed rapidly over the course of the last few years would be problematic. "It's just going to kick the can down the road, and we are going to be back to the same place we were before. But this time it will be with many more death tolls, so I just don't think it's viable."