Michael E. Leiter, who is one of the nation’s top counterterrorism officers, said on Wednesday that American intelligence officials now predicted that there were fairly no less than 300 Qaeda leaders and fighters, who had been hiding in Pakistan’s tribal areas.

This is a rare public assessment of the strength of the terrorist squad that is the central target of President Obama’s war policy.

Taken into account all the recent estimate by the C. I. A. Director, Leon E. Panetta, there are almost 50 to 100 Qaeda operatives now in Afghanistan. American intelligence agencies are of the consideration that there are most likely less than 500 members of the group in an area, where the United States has supplied almost 100,000 troops.

A number of American officials caution against such comparisons, stating that Al Qaeda has forged secure ties with a number of allied militant collections and that a big American troop presence is essential to help the Afghan Government avert Al Qaeda from being successful in gaining a safe sanctuary in Afghanistan. It is something that is similar to what it had before the Sept. 11 attacks.

Mr. Leiter, who is the Director of the National Counterterrorism Center, agreed with Admiral Mullen’s finding.