WASHINGTON  Al Qaeda’s success in forging close ties to Pakistani militant groups has given it an increasingly secure haven in the mountainous tribal areas of Pakistan, the American government’s senior terrorism analyst said Tuesday.

Al Qaeda is more capable of attacking inside the United States than it was last year, and its cadre of senior leaders has recruited and trained “dozens” of militants capable of blending into Western society to carry out attacks, the analyst said.

The remarks Tuesday by the intelligence analyst, Ted Gistaro, were the most comprehensive assessment of the Qaeda threat by an American official since the National Intelligence Estimate issued last summer, which concluded that Al Qaeda had largely rebuilt its haven in Pakistan’s tribal areas.

A year later, Mr. Gistaro said, the problem has only grown worse, in part because of a symbiotic relationship between Qaeda operatives and Pakistani militant groups based in the tribal areas.