Revelations about anthrax scientist Bruce E. Ivins's mental instability have exposed what congressional leaders and security experts call startling gaps in how the federal government safeguards its most dangerous biological materials, even as the number of bioscience laboratories has grown rapidly since the 2001 terror attacks.

An estimated 14,000 scientists and technicians at about 400 institutions have clearances to access viruses and bacteria such as the Bacillus anthracis used in the anthrax attacks, but security procedures vary by facility, and oversight of the labs is spread across multiple government agencies.

Screening for the researchers handling some of the world's deadliest germs is not as strict as that for national security jobs in the FBI and CIA, federal officials said. ....