Two weeks before the Sept. 11 terrorism attacks, a desperate FBI agent begged his superiors to launch an aggressive hunt for one of the men who would participate in the suicide hijackings, warning that "someday someone will die" because his request was denied, according to testimony before a congressional panel yesterday.

The New York special agent, testifying behind a screen to protect his identity, choked back tears as he described how he asked his Washington superiors on Aug. 29, 2001, to allow his office to join the search for Khalid Almihdhar, who would later help commandeer the aircraft that slammed into the Pentagon.

But lawyers in the FBI's National Security Law Unit refused. They said information obtained through intelligence channels -- that Almihdhar was an al Qaeda associate who had recently reentered the United States -- could not legally be used to launch a criminal investigation.

"Someday someone will die -- and [legal] wall or not -- the public will not understand why we were not more effective and throwing every resource we had at certain 'problems,' " the agent responded in a blistering e-mail to headquarters. "Let's hope the National Security Law Unit will stand behind their decisions then, especially since the biggest threat to us now, UBL [Osama bin Laden], is getting the most 'protection.' "

The agent's testimony, delivered to a stunned, silent audience at a hearing of the House and Senate joint intelligence panel, was the latest in a litany of missed clues uncovered by congressional investigators probing intelligence agencies' performance before Sept. 11. The account was reminiscent of the words of another FBI agent, Coleen Rowley, who testified last spring that headquarters officials limited attempts by the Minneapolis field office to investigate alleged Sept. 11 conspirator Zacarias Moussaoui in the weeks before the attacks.

The New York agent's dispute with Washington was included in a report released yesterday by the congressional panel. The document also provided more detail about the CIA's repeated failures to act on intelligence about Almihdhar and his frequent companion, fellow Flight 77 hijacker Nawaf Alhazmi.

The CIA monitored Almihdhar at a meeting of al Qaeda operatives in Malaysia more than 18 months before the Sept. 11 attacks, and knew at that time that he held a visa that allowed him to enter and exit the United States repeatedly. But the report found that the CIA did not adequately inform other agencies and made no effort until summer 2001 to add the names of Almihdhar or Alhazmi to immigration watch lists, even as it compiled increasingly disturbing information about his ties to al Qaeda.

One CIA cable about Almihdhar in March 2000 was marked, "Action required: None, FYI."

"There were numerous opportunities during the tracking of these two terrorists when the CIA could have alerted the FBI and other law enforcement authorities to the probability that these individuals either were or would be soon in the United States," said Eleanor Hill, staff director for the joint inquiry. "That was not done."

In another report earlier this week, Hill's investigators found that U.S. intelligence agencies had ample evidence before Sept. 11 that al Qaeda sought to launch attacks on U.S. soil, and that terrorists had frequently considered using airplanes as weapons. Earlier this year, it was revealed that the FBI failed to seek a warrant for Moussaoui's computer or pay attention to warnings from a Phoenix agent that terrorists might be training at U.S. flight schools.

"This failure is massive," Sen. Carl Levin (D-Mich.) said. "We have failure piled upon failure."

Sally Regenhard, whose firefighter son Christian was killed at the World Trade Center, said yesterday that "these people are guilty of malfeasance. They should be brought up on criminal charges. They are partly responsible for the deaths of 3,000 people."

CIA Director George J. Tenet acknowledged during closed testimony in June that the agency had made mistakes in the case and should have added Almihdhar and Alhazmi to a State Department watch list prior to August 2001, according to the panel's report.

Yesterday, officials from the FBI and CIA, while disagreeing over some details of the Almihdhar affair, testified that overwhelming workloads, ongoing terrorist threats and legal restrictions affected their responses.

A CIA officer involved in the case, who also testified behind a screen, said the errors were "the kinds of misses that happen when people, even very competent dedicated people . . . are simply overwhelmed."

Michael Rolince, a special agent-in-charge at the FBI's Washington field office, told the panel that restrictions on the sharing of information between the CIA and FBI contributed to missteps in the Almihdhar case.

"In terrorism cases, this became so complex and convoluted that in some FBI field offices, FBI agents perceived walls where none actually existed," Rolince said.

The CIA first picked up Almihdhar's trail in Kuala Lumpur in January 2000, when he was identified as a participant at a meeting of suspected al Qaeda associates. U.S. intelligence agencies were on a state of high alert to terror threats because of the arrest a month earlier of Ahmed Ressam, who was caught entering the United States from Canada with explosives in a plot to bomb Los Angeles International Airport.

But congressional investigators found that the CIA repeatedly failed to alert the FBI or others to Almihdhar and his possible connections to terror.

By the time Almihdhar first came to Malaysia, the congressional report said, the CIA knew his name, passport number, birth information and U.S. visa status. They also identified another participant as Alhazmi, whose brother, Salim, was known to authorities. The CIA didn't know that the National Security Agency had already linked Alhazmi with al Qaeda.

According to a version of events first related by CIA officials earlier this year, the agency sent a cable to CIA stations worldwide on Jan. 5, 2000, highlighting Almihdhar's travel to Malaysia and noting that his passport contained a multiple-entry visa. The CIA message said the information was being passed to the FBI. It was provided verbally the next day to an FBI agent.

But investigators said they have found no documents at the CIA or FBI indicating that the information was sent in writing to the bureau. They noted that a CIA e-mail at the time said the FBI agent was told "a lot of suspicious activity has been observed but nothing that would indicate evidence of an impending attack or criminal enterprise."

By that summer, the Malaysia meeting had faded from view at the CIA. Almihdhar and Alhazmi went about their activities unfettered that spring, using their own names on documents in San Diego, taking flight lessons and, in Almihdhar's case, flying to Frankfurt, Germany, in June. Alhazmi renewed his visa in July.

In October 2000, two al Qaeda operatives bombed the USS Cole in Yemen, killing 17. Investigators soon identified the plot's organizer as Tawfiq bin Attash, also known as Khallad. Two Cole conspirators had delivered money to Khallad in January 2000. The place: the meeting in Kuala Lumpur.

Thus, investigators noted in their report, by January 2001 the CIA knew that Almihdhar and Alhazmi had been in contact with the suspected mastermind of the Cole attack in Malaysia. Yet their names were still not added to a watch list, which would have flagged Almihdhar when he tried to return to the United States months later. CIA officials again failed to inform the FBI of the duo's entry into the country, FBI officials said.

In July, a CIA officer assigned to the FBI discovered a CIA cable chronicling Khallad's presence at the Malaysia meeting and fired off an e-mail to the CIA's counterterrorism center: "This is a major league killer, who orchestrated the Cole attack and possibly the [1998 East] Africa bombings." That message prompted another look at the Malaysia meeting, this time by an FBI analyst who discovered Almihdhar's travels and his return to the United States on July 4.

Finally, on Aug. 23, the CIA sent cables to the State Department, the FBI, the Immigration and Naturalization Service, and the Customs Service, requesting that four "bin Ladin related individuals," including Almihdhar and Alhazmi, be put on a watch list. At the same time, the FBI field office in New York, then the center of terrorism probes at the bureau, sought the criminal investigation of Almihdhar but was rebuffed.

On Sept. 11, after the World Trade Center was struck, the FBI agent and his colleagues received the passenger manifests from the four fatal flights. Yesterday he told the panel that he yelled angrily: "This is the same Almihdhar we've been talking about for three months!"

His supervisor, trying to reassure him and the others, answered back: "We did everything by the book."

A screen is used to conceal the identities of a CIA agent and New York-based FBI agent who testified before a joint panel of the House and Senate intelligence committees. The panel is investigating Sept. 11 intelligence failures.