WASHINGTON - With only three weeks left before U.S. military forces are scheduled to begin withdrawing from Afghanistan, the debate over the size and pace of that withdrawal has become increasingly intense.

Ryan Crocker, President Obama's choice to become ambassador to Afghanistan, appeared before a Senate panel Wednesday. But as the debate rages in Washington, the sad reality is that the war drags predictably on and on. (By J. Scott Applewhite, AP) On one hand, the Pentagon, backed by prominent neo-conservatives and other hawks, insists that the 18-month-old "surge" of 30,000 U.S. troops has turned the strategic tide against the Taliban.

Anything more than a "modest" drawdown of a few thousand of the nearly 100,000 soldiers and marines there through the end of the year, they argue, risks losing all that has been gained.

"I would hope that (the withdrawal) is very small," the 2008 Republican presidential candidate, Sen. John McCain, told the Financial Times this week. "I would hope that it is 3,000. We need another fighting season (against the Taliban)."

On the other hand, President Barack Obama's political advisers, backed by a strong majority of Democrats and a small but growing minority of Republicans in Congress, are arguing for a much more substantial withdrawal.

In the clearest marker so far, the influential chairman of the Senate Armed Services Committee, Carl Levin, said this week that at least 15,000 troops should be withdrawn between July and the end of the year.

His appeal came just days after the ranking Democrat on the House subcommittee that oversees the Pentagon's budget, Rep. Norm Dicks, shocked Washington by calling for an end to the U.S. military presence in Afghanistan before 2014. Current plans call for the U.S. and its NATO allies, which have sent more than 40,000 troops, to withdraw all their combat forces by the end of that year.

"We need to start seeing if we can do this (withdrawal) a little faster," Dicks, a veteran Democratic hawk, told Politico.

"I think the American people would overwhelmingly like to see this brought to a conclusion sooner than 2014," he said, citing growing "war fatigue" in Congress.

Obama, who has promised that the initial withdrawal will be "significant", has otherwise kept his cards close to his chest. The White House said he was still waiting to receive formal recommendations from the outgoing defence secretary, Robert Gates, who met with military commanders during a three-day farewell visit of Afghanistan that began on the weekend.

The withdrawal debate has intensified steadily since the May 2 killing by U.S. Special Forces of Al-Qaeda chief Osama bin Laden at a compound in the Pakistani resort town of Abbottabad where he had apparently been living for six years. Until then, it appeared that the Pentagon and its civilian allies would prevail upon Obama to withdraw only a "modest" – if not token – number of troops in July and through the end of the year.

But bin Laden's demise gave new momentum to the war's critics who have long argued that Al-Qaeda had, for all practical purposes, left Afghanistan in 2001 and that Washington's military-led counterinsurgency (COIN) strategy there was overly ambitious and largely ineffective, if not counter-productive.

"We've gone from being waist- to chest-deep in quicksand," noted Matthew Hoh, who directs the Afghanistan Study Group and served in Afghanistan as both a Marine captain and a State Department adviser.

At the same time, the growing focus in Congress about the yawning government deficit has cast a harsher light on the war's enormous cost – some 10 billion dollars a month, not including another 300 million dollars a month for civilian-led aid projects.

It was these considerations, as well as unhappiness with U.S. military operations in Libya, that led late last month to near- passage by the House of Representatives of an amendment to the 690- billion-dollar 2011 defence authorisation bill that required Obama to submit a plan for withdrawing U.S. troops and "an accelerated transition" of U.S. operations there to the Afghan government.

The amendment, which was defeated 204-215, gained the votes of all but eight Democrats and 26 Republicans – a total of nearly 42 more votes than a similar measure last year.

The vote, which was taken as a strong indication of war weariness, appears to have tilted the balance in the debate, as the Pentagon and its backers stepped up their public campaign for a "modest" withdrawal of just a few thousand troops beginning in July.

Thus, a Washington Post/ABC poll released earlier this week that showed a sharp increase - from 31 percent last March to 43 percent after bin Laden's death - in the percentage of people who believe that the war in Afghanistan has been worth the costs was seized on by one former Bush administration adviser as evidence that Obama "probably has the political breathing room" to choose a "measured withdrawal" as opposed to a "rapid retreat".

The same survey, however, showed found that three out of four respondents favoured withdrawing "a substantial number of U.S. combat forces from Afghanistan this summer".

At the same time, Kimberly and Frederick Kagan, neo-conservative military analysts close to the outgoing U.S. commander in Afghanistan, Gen. David Petraeus, published an op-ed in the Wall Street Journal arguing that "nothing about conditions on the ground justifies the withdrawal of any U.S. or coalition forces".

Moreover, they warned, if Obama withdraws all 30,000 "surge" forces by the end of 2012, "the war will likely be lost."

Gates, who has called for a "modest" drawdown, has not offered a specific number, but, since the House vote, in particular, he has made clear that he wants as few combat troops as possible to leave.

"I think we shouldn't let up on the gas too much, at least for the next few months," he said over the weekend. He has also hinted that he will speak out publicly in support of the current strategy after he steps down at the end of the month.

Whether this will be enough to sway Obama, who has been criticised by his fellow-Democrats for deferring too much to the military, remains to be seen.

But it is clear that disillusionment with the war is spreading in both parties.

Releasing a highly critical staff report on the effectiveness and sustainability of U.S. aid programmes in Afghanistan Wednesday, Senate Foreign Relations Committee Chairman John Kerry expressed strong doubts about the current strategy.

"While the United States has genuine national security interests in Afghanistan," said Kerry, a key foreign policy ally of the White House, "our current commitment, in troops and dollars, is neither proportional to our interests nor sustainable."

His remarks were seconded by the Committee's ranking Republican, Sen. Richard Lugar. "Despite 10 years of investment and attempts to better understand the culture and the region's actors, we remain in a cycle that produces relative progress but fails to deliver a secure political or military resolution," he said.

"Undoubtedly, we will make some progress when we are spending more than 100 billion dollars per year in that country. The more important question is whether we have an efficient strategy for protecting our vital interests that does not involve massive open-ended expenditures and does not require us to have more faith than is justified in Afghan institutions," he said.