In August, Congress provided a temporary extension and fix to the current wiretapping law. "We're better prepared now to continue our mission," McConnell said of the move.
Asking the members of Congress to keep those authorities in place, McConnell said, "If we lose FISA, we will lose, my estimate, 50 percent of our ability to track, understand and know about these terrorists, what they're doing to train, what they're doing to recruit, and what they're doing to try to get into this country."
Chertoff also illustrated several incidents that have raised concerns for his department. In May, a passenger name record (PNR) hit alert alerted U.S. customs officials that a citizen of the United Kingdom should not be allowed to board an aircraft, and the individual was subsequently turned over to U.K. authorities for questioning.
An April PNR hit alerted U.S. Customs officers to two passengers at Boston's Logan Airport. One or both had suspected financial ties to al Qaeda. The men were found with a CD entitled "mujahideen."
At Monday's hearing, Chertoff announced new requirements on general aviation coming from overseas to screen air crews and passengers, in an effort to identify more individuals who may pose a threat before they are allowed to travel.
"We haven't looked at the question of general aviation coming from overseas as a potential vector through which weapons of mass destruction or people who were dangerous might be smuggled into the country," Chertoff said.
"We are now working to plug that threat. Later today, we will be unveiling a plan to begin the process of increasing our security for overseas general aviation coming to this country substantially," he added.
Chertoff also made reference to small boats causing more concern, a point he raised in an interview with ABC News' Pierre Thomas last Friday.
"We're looking at small boats, which would be another way of threatening our ports, aside from the container ships that we've talked about so much," Chertoff told ABC News. "And we've begun a project to screen for radioactive material in small boats."
In that interview, Chertoff maintained that there's no "credible evidence about an imminent threat in a specific way to this country that would cause us to raise the level." On Monday, he said it's "no mere accident and not just luck" that the United States has not been attacked since 9/11.
Mueller acknowledged the findings of a Justice Department inspector general report released last week, saying one area the FBI needs to improve is "quality assurance. The information that we get -- assuring that it is updated so that persons who may have been on the list at some point in time when we have additional information are removed from the list."
The report also found that the Terrorist Screening Database has grown at an increasingly rapid pace, adding to analysts' workloads. "Since April 2004, the TSDB has more than quadrupled in size, growing from 150,000 to 724,442 records in April 2007," it stated. As many as 400,000 individuals suspected of terrorism are listed in government databases, Redd said.
In one of the more damaging findings, the report also noted that a computer glitch kept the names of at least 20 known or suspected terrorists off the list.