WASHINGTON - As he mulls how many U.S. troops to pull out of Afghanistan starting next month, President Obama is coming under increasing pressure from Democratic lawmakers as well as a growing number of Republicans to reexamine his war strategy after the killing of Osama bin Laden.

The president's nominee to be the new U.S. ambassador to Kabul, veteran diplomat Ryan Crocker, felt the heat Wednesday.

Senate Foreign Relations Committee members of both parties used Crocker's confirmation hearing to vent frustration with the persistent violence in Afghanistan nearly a decade after the U.S. invasion, and to question the size of the U.S. military contingent there and what nearly $19 billion in U.S. aid since 2001 has accomplished.

Before the hearing, the panel's majority Democrats released a two-year study highly critical of U.S. aid programs. It found that the $320 million now spent each month lacked oversight, had limited impact, and was fueling corruption and diverting skilled Afghans into U.S.-funded projects, depriving their government of their talents.

"While the United States has genuine national security interests in Afghanistan, our current commitment in troops and in dollars is neither proportional to our interest nor sustainable," said the committee chairman, John Kerry (D., Mass), who until recently was a backer of the administration's policy.

"What we're doing . . . is not sustainable," agreed Sen. Bob Corker (R., Tenn.).

Yet Obama is trapped between the unrelenting bloodshed in Afghanistan - and an allied insurgency destabilizing nuclear-armed Pakistan - and domestic demands that he bring American troops home, reduce unemployment, and close the budget deficit, all critical to his 2012 reelection prospects.

Waiting for Petraeus

With polls showing Americans opposing the war, some Obama aides are advocating a major troop drawdown.

Defense Secretary Robert M. Gates and U.S. military commanders, however, fear that a precipitous U.S. drawdown will spur greater violence and encourage leaders of the Taliban and allied groups to spurn peace talks being sought by the United States, the NATO allies, and Afghan President Hamid Karzai.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said in an interview Wednesday that the military would craft several drawdown options based on recommendations from Army Gen. David H. Petraeus, the top commander of U.S.-led forces in Afghanistan.

"Gen. Petraeus has made no specific submission to this point, and we all wait for him to do that. And that will really trigger the process of review," Mullen said during a trip to the Middle East and Europe. "My expectation is that there will be several options and the risks associated with the options."

Crocker, a former U.S. envoy to Iraq whom Obama pulled out of retirement, acknowledged enduring problems of bad governance, corruption that "undermines the credibility of the Afghan state," narcotics trafficking, and a dearth of basic services.

But he insisted that there had been progress, and he warned that walking away from Afghanistan, as the United States did after the 1979-89 Soviet occupation, could bring "disastrous consequences," a reference to the Sept. 11 attacks that al-Qaeda organized from there.

The hearing came as Obama weighs how many of the 100,000 U.S. troops to withdraw from Afghanistan beginning next month. He set the deadline in a Dec. 1, 2009, speech laying out a strategy to "disrupt, dismantle, and defeat" al-Qaeda and prevent a Taliban takeover that would allow the terrorist network to return to Afghanistan.

The strategy deployed an additional 30,000 U.S. troops, mostly in the Taliban's southern strongholds of Kandahar and Helmand provinces, and stepped up training to create 300,000-strong Afghan security forces. It also increased U.S. aid to improve governance and spur employment and services to boost backing for Karzai's government.

Nearly 18 months later, bin Laden is dead, killed in a May 2 U.S. raid on his hideout in Pakistan.

The start of the drawdown coincides with the transfer of security responsibilities for seven provinces and districts to Afghan forces, a process scheduled to culminate in 2014 with a total withdrawal of U.S.-led NATO troops.

Poll findings

A Washington Post-ABC News poll released Tuesday found that 73 percent of Americans favored a "substantial" withdrawal of U.S. forces beginning next month.

Many Republicans, including Sen. John McCain of Arizona, the top GOP member of the Armed Services Committee, back Gates and his commanders, who want a token withdrawal this year.

"I hope the administration listens to Secretary Gates," McCain told McClatchy. "He sees a careful drawdown and said it would be 'premature' to change course."

Asked about a call for a withdrawal of 15,000 soldiers by Sen. Carl Levin (D., Mich.), the committee's chairman, McCain replied: "If you want to lose, you do that."

A top Republican on the Foreign Affairs Committee questioned that approach.

"Undoubtedly we will make some progress when spending more than $100 billion per year in that country," said Sen. Richard G. Lugar of Indiana. "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."

'Safe haven'

Kerry, voicing concerns that officials express privately, pointed out that U.S. policy has failed to deal with the sanctuaries enjoyed by the Taliban, al-Qaeda, and allied extremists in Pakistan's tribal area bordering Afghanistan.

"We're spending $120 billion [a year] in a country [Afghanistan] where there is no safe haven and about $2.8 billion in a country [Pakistan] where there is a safe haven," he said.

The two-year study of U.S. aid found that assistance was geared mostly toward projects with short-term results, such as paying Afghans in areas previously controlled by insurgents to repair irrigation canals or repair roads in order to win popular support and encourage locals to share intelligence with U.S. forces.

But the funds aren't producing long-term employment or development and have created a "war economy" that could collapse into a "severe economic depression" after foreign forces leave, it warned.