F.B.I. officials repeatedly complained to the spy agency, which was collecting much of the data by eavesdropping on some Americans' international communications and conducting computer searches of foreign-related phone and Internet traffic, that the unfiltered information was swamping investigators. Some F.B.I. officials and prosecutors also thought the checks, which sometimes involved interviews by agents, were pointless intrusions on Americans' privacy.

"We'd chase a number, find it's a school teacher with no indication they've ever been involved in international terrorism - case closed," said one former FBI official, who was aware of the program and the data it generated for the bureau. "After you get a thousand numbers and not one is turning up anything, you get some frustration."

F.B.I. field agents, who were not told of the domestic surveillance programs, complained they often were given no information about why names or numbers had come under suspicion. A former senior prosecutor, who was familiar with the eavesdropping programs, said intelligence officials turning over the tips "would always say that we had information whose source we can't share, but it indicates that this person has been communicating with a suspected Al Qaeda operative." He said, "I would always wonder, what does 'suspected' mean?"

In response to the F.B.I. complaints, N.S.A. eventually began ranking its tips on a three-point scale, with 3 being the highest priority and 1 the lowest, the officials said. Some tips were considered so hot that they were carried by hand to top F.B.I. officials. But in bureau field offices, the N.S.A. material continued to be viewed as unproductive, prompting agents to joke that a new bunch of tips meant more "calls to Pizza Hut," one official, who supervised field agents, said.