The decline is mostly the result of the bureau's heavy focus on terrorism investigations in recent years.
The Sept. 11, 2001, terrorist attacks on U.S. soil changed the FBI's focus, but other agencies that are heavily engaged in white-collar criminal investigations are showing similar changes, says the study by the Transactional Records Access Clearinghouse, a private group at Syracuse University.
A top FBI official said the agency's new emphasis on stopping terrorists was necessary - and effective.
"To say the FBI is a shadow of its former self is to ask the question: What do you get for shifting FBI agents to the national security mission?" said John Miller, an assistant FBI director. "If the answer is going 6 1/2 years without a successful attack by terrorists on U.S. soil, then I think it's a win."
The flip side to the declines is the soaring number of immigration investigations, which now account for more than a quarter of all criminal referrals to the Justice Department, according to TRAC.
Last year, 41,600 immigration cases went to the Justice Department for possible prosecution, more than double the figure from 2001. The latest figure is four times the number of two decades ago.
At the FBI, the bureau accounts for less than one of every six case files referred to the Justice Department for possible prosecution. Twenty years ago, it was more than one out of every three, says TRAC, which based its findings on the government's own data. TRAC obtained the data under the Freedom of Information Act.
"We're doing fewer low-end fraud and drug cases, the easy lay-ups," said Miller, the FBI official. "At the same time hundreds of agents worked on Enron, HealthSouth, Qwest. Another priority, complex public corruption cases, may take two years, but the result is an achievement that transcends arrest numbers."
Other federal law enforcement agencies that are seeing dramatic declines in referrals include the Secret Service, Internal Revenue Service and the U.S. Postal Inspection Service.
Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., said "there is no question about the importance of the FBI's work in fighting terrorism. But we must be mindful of the traditional and critical role the Bureau plays in domestic law enforcement, and we must reverse the trend of shifting important resources away from investigating violent crime and white collar crime."
The federal data that TRAC collected from the Justice Department's Executive Office of U.S. Attorneys states that:
-The FBI made 25,100 criminal referrals last year, compared to 41,300 in 1987.
-Last year, the FBI made 2,300 referrals to the Justice Department in white-collar investigations, an 82 percent decline from 2001. White-collar referrals peaked at 20,900 in 1993, the year of the first terrorist attack on the World Trade Center in New York.
-At the Secret Service, the agency sent 12,200 investigations to the Justice Department for possible criminal prosecution in 1987. Now it's 5,100.
-At the U.S. Postal Inspection Service, the referral number was 6,600 two decades ago, in contrast to 5,100 now.
-At the Internal Revenue Service, the 1987 referral figure was 3,300. Now it's 2,600.
The agencies with declines say that it takes time to conduct complex criminal investigations in the Internet age against technically sophisticated targets.
A tax investigation takes an average of 507 days and "we've been tackling a higher proportion of cases that take longer," says Victor Song, the IRS deputy chief for criminal investigations.
The anthrax attacks of 2001 prompted the U.S. Postal Inspection Service to strengthen its focus in the security arena, but "we have not shifted resources" away from other investigations, said Douglas Bem, a spokesman for the service.
"Many of our cases are prosecuted at the state and local level when it's more appropriate rather than through the federal judicial system," said Bem. "We work at all levels, not only with U.S. attorneys."
Investigations involving cyber crimes, especially network intrusions, are much more complex than the investigations of 20 years ago and cases are often global in scope and tend to be longer running, says Secret Service spokesman Edwin Donovan.