"We should be willing to spend more if we get better returns - and less if we don't," said Sen. Joseph Biden, chairman of the Senate Foreign Relations Committee.
A recent independent audit concluded the U.S. has little proof that the $5.6 billion given to Pakistan to go after terrorists since 2001 has been used for that purpose. At the same time, Biden said, not enough is being done to build schools, hospital clinics and roads in the border region, where extremists have found refuge.
"We believe we're paying too much and getting too little. The Pakistanis believe exactly the opposite," said Biden, D-Del.
"Both sides feel that the costs of the relationship may soon outweigh the benefits" he added. "The status quo is unsustainable."
Assistant Secretary of State Richard Boucher said the administration was open to considering Biden's approach.
"While we do not agree on every point in the current version of the proposed legislation, we welcome this initiative and feel strongly that a new, bipartisan commitment to partnership with Pakistan is crucial," Boucher told the committee.
Boucher testified on the heels of a Government Accountability Office study that found, for example, that the U.S. recently gave Pakistan more than $200 million for air defense radars without bothering to investigate whether the money was needed specifically to go after terrorists.
The U.S. has given Pakistan a total of $10.8 billion in economic and military aid since the Sept. 11 terrorist attacks.
U.S. officials have responded that better controls over military reimbursement payments are needed. But, they add, the value of the aid program should not be underestimated because many terrorists have been captured or killed with Pakistan's help.
Pentagon press secretary Geoff Morrell said Wednesday that the money is well spent and that Pakistan provides sufficient clarity on how the funds are used. He said people may be trying to impose "Wall Street accounting standards" on a process that involves a sovereign nation.
"This is reimbursement for military operations that they (the Pakistanis) are conducting, really on our behalf, in an area of the world that we cannot operate (in) at this point," Morrell said, adding that the spending is reviewed at several points in the process.
While he said the Pentagon is always looking for ways to improve the auditing process, he also said that paying the Pakistanis to conduct the operations is significantly cheaper than it would cost for the U.S. to do it alone.
Boucher told the committee Wednesday that he sees promise in a forthcoming anti-terrorism agreement among Pakistan's political and military leaders.
The agreement, expected to be announced shortly by Pakistan's prime minister, should make clear that Islamabad plans only to negotiate with tribal leaders along the Afghan border and not with the militants, Boucher said.
Pakistan's leaders have said in the past this was their policy, but some have negotiated directly with insurgents - an approach that resulted in an increase in violence and cross-border attacks into Afghanistan, according to Boucher.
"Certainly the approach of saying, 'We will work with the tribes to kick out the terrorists' is a better approach than going directly to negotiate with militants," Boucher later added. "And that seems to be the approach they are adopting, not one that they have implemented successfully yet."