Two truths about lie detectors:

1. Experts prefer the term "polygraph test" over "lie detector."

2. They say the examination cannot be cheated on.

Some fears about lie detectors:

1. An uncomfortable vision of being strapped to a machine, watching a needle jump around if you breathe the wrong way, beads of sweat forming on your forehead, giving you away.

2. The growing use of the machines by industry and government employers, like the D.C. police, conjuring up again the specter of "1984."

The Great Debate:

Whether William Casey, the director of the Central Intelligence Agency, and James Baker, the White House chief of staff, will be asked to take polygraph tests as part of the Carter-Reagan debate papers investigation.

Washington has long been a center for the Big Lie Detector Controversy. It was a case argued here in 1923, Frye v. United States, that rejected the results of a precursor of the polygraph as evidence. Polygraph results are not admissible in federal courts and many state courts, and the District has one of the stiffest laws, forbidding employers to use the tests. And it was a Capitol Hill sage, former senator Sam Ervin, who called the tests "a 20th-century instrument of witchcraft."

The debate over the reliablity and application of the polygraph was renewed this year when President Reagan issued a directive, since limited by Congress, making lie detector tests a condition for federal employes with security clearances. Also heating up the controversy: the possible use of polygraph tests in the debate papers caper; and a claim by a high-ranking Defense Department official, who once said polygraphs "misclassified innocent people as liars," that Soviet spies were being trained to fool the tests.

In an internal memo disclosed last month, John F. Beary III, assistant secretary of defense for health affairs, said, "I am told the Soviets have a training school where they teach their agents how to beat the polygraph."

A few days later, James Hamilton, the special counsel hired in the congressional probe of the purloined papers and the conflicting statements of Casey and Baker, was quoted as saying he doubted the polygraph tests could clear up the discrepancies. Yesterday Hamilton said, "The chairman has not decided whether to seek lie detector tests. In some cases it can be fairly useful."

Polygraph examinations usually take more than an hour. They begin with an interview, where the examiner sets a rapport with the person being tested. Then the questions. The first set is neutral, with such questions as "What is your mother's name?" This establishes the norm of truth, the subject's physical reactions to nonstressful questions. Then in the key questions, the examiner watches for signs of stress, such as changes in pulse rate or breathing.

"Polygraph examiners dislike the term 'lie detector.' It supposes deception," says Raymond Weir Jr., past president of the American Polygraph Association and one of Washington's best-known polygraph examiners. But the "Lie Detector" show, which flamboyant criminal lawyer F. Lee Bailey briefly brought to television earlier this year, selected the objectionable term for the show, as does the strict District law regarding their use, and Weir admits the television exposure hasn't hurt the industry.

The experts discount the theory that you can put yourself in a happy or angry frame of mind--think only pleasant thoughts, or wear a too-tight pair of shoes (causing you to wince), stay up for three nights, fast, or answer in a monotone--all this to keep the emotional response constant.

These countermeasures, says psychologist David Raskin of the University of Utah, generally are ineffective. "What is potentially effective are the physical matters, biting your tongue, pressing down your toes at particular points." But the rub, says Raskin, who did a government study on the counter techniques, is you have to have coaching to know how to use them. "A person just doesn't stumble on this. You have to be trained to turn off and on, do it unobtrusively, because there are ways of detecting their use."

Other experts agree. "Trying to beat the test is counterproductive. People become more relaxed, more confident, and are more willing to discuss things in an open way. The more the feeling you can beat it is exposed, the less people will be able to beat it," says James Starrs, a law professor at George Washington University.

Weir, a former director of internal security for the National Security Agency who has done thousands of the examinations since he started in 1951, adds, "If such a thing were possible, the criminal element would have had it beat a long time ago."

Weir, who gave a test to the chief witness against former Georgia senator Herman Talmadge during the Senate investigation into charges of misconduct (for which he was later denounced), says testing Casey and Baker with the polygraph would be "exceedingly appropriate."

How accurate are the tests? "It is still an open subject," says Barton Ingraham, associate professor of criminal justice at the University of Maryland. The skeptics claim 20 to 50 percent of the tests are in error; the proponents, such as Utah's Raskin, said polygraph tests are "90 percent accurate, and that is talking about optimum conditions. If you have examiners who are not competent or trained, if you have poor issues, your rate is going to drop."

There's another school of thought. "Some statistics say that the tests are accurate in excess of 85 percent, and that sounds good," says Starrs. "But then some will say that is laboratory testing, and what counts is reality testing. The question becomes, for a lawyer and forensic scientist, whether the present state of the art in polygraph testing is such that its results should be admissible in the court of law." Starrs says no.

Then there is the human element. Are the examiners competent? They should have, says Starrs, "a natural bent, savoir-faire, rapport. They have to be able to ask you questions. If you pace them with five-second intervals, the person doesn't have a chance to respond and throws the procedure off."

"Polygraph tests work every day all over the country," says Weir. "I don't know if there has ever been any evidence that they don't work. The commercial examiners are performing services for corporations, and hard-headed businessmen wouldn't pay for them if they didn't work." In the mid-1970s, before the District law against their use by private employers, tests were used at Clyde's restaurant in Georgetown, and thefts there were considerably reduced.

Like everything else in Washington, polygraphs are the victims of political cycles.

Take the Baker and Casey controversy. Baker has claimed that Casey gave him the Carter debate briefing papers, while Casey has denied it.

John Shattuck of the American Civil Liberties Union, an opponent of polygraph tests, says, "we do not approve of the lie detector being used for Jim Baker, not even for William Casey, as we would disapprove its use on the lowest government employes. It violates all their rights."

Weir says testing Baker and Casey might work. "It is fairly reasonable to assume that one of their statements is not true, barring a lapse of memory," he says.

Ingraham of Maryland says he thinks the implications of the debate papers case are too important to rely on lie detectors. "The costs of being wrong in that situation are so great," he says. "The machine is just too unreliable."

Raskin of Utah, who is studying the polygraph accuracy for the Office of Technology Assessment, thinks the use is appropriate but doesn't know if the results will successfully answer the remaining questions. "It would depend on how clear those issues are in their minds. If Baker says he is very clear, then he is testable." If Casey doesn't remember, "that becomes problematic. I guess he could be tested in relation to the specific statements made by Baker."