PROBE THREATENS FBI LAB REPUTATION : AGENT WILL NOT BE CALLED TO TESTIFY IN OKLAHOMA CITY BOMBING TRIAL.

Byline: David Johnston and Andrew C. Revkin The New York Times

For decades the FBI's reputation as a crime-fighting agency has rested heavily on its high-tech forensic laboratory, which could solve baffling crimes from a speck of blood, a sliver of paint or the thinnest filament of human hair.

But an investigation by the Justice Department's inspector general has put the FBI laboratory, and the way the agency has used it, under the glare of public scrutiny. The findings, which were turned over to FBI officials last week, are threatening to shatter the image of an agency on the cutting edge of scientific sleuthing.

On Monday, FBI officials announced a shake-up at the lab, transferring four senior employees, including the heads of the chemistry and explosives units, the first in disciplinary personnel actions in what officials say will be a thorough overhaul of the lab's operations.

And Tuesday, three senior FBI agents who evaluated evidence in the Oklahoma City bombing case were removed from their jobs in the bureau's crime lab as a result of the Justice Department's investigation, The Associated Press reported.

As a result of problems uncovered by that probe, federal prosecutors have decided against calling one of the three as an expert witness on explosive residues when Timothy McVeigh goes on trial in March for the 1995 truck-bombing that killed 168 people, officials said.

``It's the worst self-inflicted wound since President Nixon released the White House tapes'' during the Watergate scandal, said McVeigh's attorney, Stephen Jones.

Justice Department officials, speaking on condition of anonymity, expressed confidence other experts can present all the forensic evidence they will need in the Oklahoma City case.

The full Justice Department report has not yet been made public, but current and former FBI lab officials who have been interviewed by the inspector general's office have said that dozens of other cases have been affected by problems associated with the lab's work.

Among the problems cited by the officials were sloppy handling of evidence and lax procedures within the lab. In addition, they complained of the work of agents who use the lab to make their cases, including unreliable processing of the material sent to the lab for analysis and misuse of the lab's findings by FBI agents and their supervisors.

This range of problems has been evident in several well-known cases:

After federal agents searched the residence of Richard Jewell, a private security guard who was an early suspect in a bombing at the Atlanta Olympics last summer, FBI scientists and other specialists warned that ``you've got the wrong guy,'' an FBI laboratory official said. But their cautionary remarks, based on the absence of even trace amounts of explosive materials, went unheeded for months.

During the investigation of the 1993 bombing of New York's World Trade Center, some investigators in the chemistry section of the FBI lab became concerned that tests being conducted for traces of an explosive blend of urea and nitrogen fertilizer were not precise enough.

Errors at the lab are already providing defense lawyers with ammunition to use in some of these cases and appear to threaten the FBI with challenges to expert forensic testimony in cases based on the more than 600,000 evidence examinations conducted each year by the lab. The problem could expand beyond federal cases to affect evidence in thousands of state and local cases examined by the FBI each year.

On Tuesday, FBI officials began trying to limit the damage to the lab's reputation, issuing a report on efforts to improve the lab. The agency is improving training and building a new lab at its training academy in Quantico, Va., to replace the lab now housed at FBI headquarters in Washington.