The Obama administration has been pressing Karzai to sign a pact that would authorize US troops to remain in Afghanistan after 2014. Karzai has refused to sign so far, although Washington insists a deal must be approved before it will agree to leave a contingent of troops in Afghanistan.
"It's my own view, not necessarily company policy... I don't believe that President Karzai is going to sign it," said National Intelligence Director James Clapper, the highest level US official to express such strong doubt, at a US Senate hearing.
When asked if it would "clear the air" if the United States were to declare it would just wait for the next Afghan president to sign the security agreement, Clapper said it could be positive.
"It could have a salutary effect, I suppose, if we said that," he told the US Senate Armed Services Committee.
The United States and other nations have been seeking to keep thousands troops in Afghanistan for counterterrorism and training of Afghan personnel after US forces formally withdraw at the end of 2014. The action would end a 13-year mission in Afghanistan that began after the September 11, 2001, attacks.
In the absence of a bilateral agreement, the White House says all US forces will withdraw at the end of the year, and that a decision from Karzai is needed within weeks.
Karzai has called that an empty threat and suggested any security deal could wait until after his country's April elections. Afghanistan's constitution bars Karzai from running for a third term.
WHITE HOUSE STANDS FIRM
The Wall Street Journal reported on Monday that the United States was considering waiting until Karzai leaves office before completing the pact and deciding on a troop presence beyond 2014. The White House said it was standing by its previous comments on the issue.
Lieutenant General Michael Flynn, director of the Defense Intelligence Agency, said there would be consequences from a delay.
"The level of uncertainty, the potential loss of confidence by the people of Afghanistan, by the Afghan national security forces, you know, is a real problem," Flynn said.
Karzai's failure to sign the agreement is just one issue fueling tension in US-Afghan relations.
Separately, US forces in Afghanistan on Tuesday condemned Kabul's decision to proceed with plans to release additional detainees that Washington believes pose a continuing militant threat.
Senator Carl Levin, the Michigan Democrat who is chairman of the committee, criticized Karzai during the hearing.
"Whoever the next Afghan president is, he is likely to be more reliable than President Karzai, and his signature is likely to instill more confidence than would Karzai's signature," Levin said.
South Carolina Republican Senator Lindsey Graham promised to introduce a Senate resolution soon, condemning the prisoner release and cutting off some aid to Afghanistan.
"I will be urging my colleagues to cut off all developmental aid to Afghanistan as a response until after the next election," Graham said.
(Reporting by Patricia Zengerle; Editing by Bill Trott, Meredith Mazzilli and Gunna Dickson)