Washington — U.S. federal agencies should not rely on lie detectors to screen workers and job applicants because the machines simply are too inaccurate, the National Research Council said Tuesday.

"The belief in its accuracy goes beyond what the evidence suggests," Stephen Fienberg of Carnegie Mellon University said at a news conference.

Mr. Fienberg, chairman of a research panel that studied the use of polygraphs, said depending on the machines could create a false sense of security.

"Overconfidence may lead, in turn, to the neglect of other methods of ensuring safety, such as periodic security reviews," Mr. Fienberg said.

Kathryn Laskey of George Mason University said agencies that depend on the machinery face tough decisions in applying the results of the tests.

"It's a difficult choice between misidentifying truthful individuals as security risks and allowing national security dangers to go free," Ms. Laskey said. "These are tough choices."

"We stress, though, that no spy has ever been caught using the polygraph," she added.

In its report, the council concluded: "Almost a century of research in scientific psychology and physiology provides little basis for the expectation that a polygraph test could have extremely high accuracy."

The research council, an arm of the National Academy of Sciences, prepared the study at the request of the Energy Department. Under the law, workers in sensitive positions in department labs are subject to polygraph screening.

The department said it would carefully review the report on what it called a "very complex subject."

The Research Council recommended more research into methods of lie detection.

Polygraphs measure heartbeat, blood pressure and other factors that are known to change when people are under stress, as they are when they lie.

People can learn to control those responses to "beat" a lie detector, the report said.