Spy Agency Data After Sept. 11 Led F.B.I. to Dead Ends

By LOWELL BERGMAN, ERIC LICHTBLAU, SCOTT SHANE and DON VAN NATTA Jr.

WASHINGTON, Jan. 16 - In the anxious months after the Sept. 11 attacks, the National Security Agency began sending a steady stream of telephone numbers, e-mail addresses and names to the F.B.I. in search of terrorists. The stream soon became a flood, requiring hundreds of agents to check out thousands of tips a month.

But virtually all of them, current and former officials say, led to dead ends or innocent Americans.