Isaf commanders argue that freezing numbers will give them more time to mentor and train the 350,000-strong Afghan army and police force.
General Dan McNeill, the American commander of ISAF, has given warning that the alliance's future is at stake in the country.
Pakistan military sources confirmed the US rescuers flew into Islamabad from Afghanistan, where they are part of the Nato-led International Security Assistance Force (ISAF), soon after the US embassy announced it was prepared to give any assistance sought.
ISAF has secured the streets of the capital, and the cruising khaki cars and tanks give people welcome reassurance.
General McChrystal's presentation to Nato defence ministers and Isaf representatives provided an uncompromising obstacle to Mr Obama's plan to bring troops home in time to give him a shot at a second term, according to senior military sources.
This year's fighting season, which is now underway, has shown that the Taliban is still strong, despite the pounding given to them over the winter by ISAF forces.
But the report underscored just how difficult it is for ISAF to have confidence in the government's assurances, given the reality at Afghan detention facilities.
Yet at a classified meeting six months ago at the Isaf headquarters, General Stanley McChrystal, the then Nato commander, was given a dossier on Ahmed Wali Karzai's malpractice by officers who wanted him removed.
"The weakness of state institutions, malign actions of power brokers, widespread corruption and abuse of power by various officials, and ISAF's own errors, McChrystal wrote in a 66-page report to Gates, "have given Afghans little reason to support their government".
"So instead of Isaf going out to take the fight to the enemy, it's the ANA (Afghan National Army) and Afghan police giving the security, and that's a huge change.
