The situation in Afghanistan is dire, and progress will demand a substantial and sustained commitment, military leaders told Congress Wednesday, as they laid out more details of the Obama administration''s new strategy for the war.

But skeptical members of the Senate Armed Services committee pressed the defense officials about the pace of U.S. troops deploying to the war, and why there are no clear benchmarks on which to gauge whether the new strategy is working.

"How will we know if we''re winning?" asked Sen. Susan Collins, R-Maine. "We should not be committing additional troops before we have a means of measuring whether this strategy is successful."

Michele Flournoy, under secretary of defense for policy, said the administration is working on finalizing a set of benchmarks, but moved quickly to send some additional troops to the war because of the urgent need to reverse momentum gained by insurgents.

She and Gen. David Petraeus, commander of the troops in Afghanistan and Iraq, also urged senators to support funding to train Pakistani forces to fight militants. And they painted a somewhat pessimistic picture, saying that building the Afghan security forces and bolstering the Pakistani military to fight insurgents on their side of the border will take more time and money.

Defense leaders did not detail what the budget request would be, but said a key element will be the fund to train Pakistani forces in counterinsurgency operations that would target al-Qaida safe havens along the ungoverned Afghan border.

During the hearing on President Barack Obama''s new strategy expanding the Afghan campaign, senators also questioned how willing the Pakistani government is to take on that fight against the extremists who use the border as a staging area for attacks.