The laboratory that analyzed drug tests for thousands of airplane pilots and railroad employes has done such sloppy work that it may be stripped of those duties, sources said yesterday.

An investigation by the Transportation Department's inspector general has raised questions about the future of the laboratory, which is operated by the Federal Aviation Administration as part of the Civil Aeromedical Institute (CAMI), as well as Transportation's plan to begin a drug-testing program among thousands of its employes.

Rep. Thomas A. Luken (D-Ohio), who has scheduled a hearing today to look into the lab's performance, said that the Transportation Department's plan to conduct drug tests on thousands of agency employes may have to be reevaluated.

"If the facts are borne out that the FAA tolerated a lab which was clearly incompetent, then I think the question of suspension of further testing {by the Transportation Department} is one we'll be looking at."

The Forensic Toxicology Research Unit, as the laboratory is called, is a small part of the CAMI operation headquartered in Oklahoma City and has tested thousands of blood and urine samples for the National Transportation Safety Board's accident investigations. Since last year, the lab has also conducted drug tests for the Federal Railroad Administration on more than 750 railroad accidents.

The report found that several employes complained about the quality of work done by the lab. Earlier this year, after irregularities were found in drug tests conducted after the Conrail-Amtrak accident at Chase, Md., in which 16 people were killed, an investigation into the laboratory's methods began and the lab's director, Delbert J. Lacefield, was reassigned.

Last month, Lacefield pleaded guilty to three counts of falsifying government documents after investigators found he had reported in writing that blood tests taken in three separate railroad accidents were negative, when the tests were never performed. Lacefield, a 20-year FAA employe, resigned two weeks ago.

At the time, federal officials in Oklahoma City said that the scope of the investigation was limited to 20 drug-test cases for which Lacefield had written reports.

But documents obtained from the investigation showed that questions about the laboratory's performance had been raised a year ago.

"At present, quality control is performed in a very unstructured manner," the Armed Forces Institute of Pathology (AFIP) wrote last June 25 in a two-page memo to Dr. Frank H. Austin, then the FAA's federal air surgeon.

Austin was reassigned earlier this year after he was criticized for being too lax in issuing special certificates to pilots who failed annual medical exams.

The AFIP laboratory also noted that the CAMI lab lacked equipment needed to perform blood plasma tests, although it reported that the equipment was apparently on order. Federal prosecutors in Lacefield's case said the reason he did not perform the tests was that the lab lacked both the equipment and the expertise.

Last month, after the laboratory's problems began to become public, Transportation Secretary Elizabeth Hanford Dole complained to FAA Administrator Donald D. Engen that she was "particularly disturbed" that his agency had failed to act when many of the problems had been brought to light last summer. In an April 20 memo to Engen, Dole asked for a detailed list of all personnel changes that will occur. "On the latter point, it is clear that a complete change in the management personnel of CAMI must occur at once," Dole wrote.

Dr. Robert Dille, CAMI manager, was recalled to FAA headquarters here May 18 for a temporary 120-day assignment while two independent reviews of the lab were made.

Stephen D. Hayes, an FAA spokesman, said the reviews are complete, but the reports are not finished. Hayes said he does not know what the lab's future is, but noted that the lab is only a small part of the CAMI operation.

The lab will likely perform research, rather than analyze drug tests, in its new role, sources said. NTSB investigators said they have long suspected something was remiss with results from tests analyzed by the lab. One investigator said he worried about whether the right procedures were followed or the equipment was properly calibrated.