Things heated up at the 6th World Congress of Sexology yesterday, as Dr. William H. Masters and Virginia E. Johnson answered charges that they had made exaggerated claims for their pioneering work in the field of sex therapy.

His voice agitated and his jaw taut, Masters defended the book "Human Sexual Inadequacy"--and the initial 10 years of therapy it described--as a "product of the times."

"This was a beginning episode in sex therapy," Masters told a tempestuous gathering of reporters and colleagues during a lunchtime recess at the Washington Hilton. "Let me use the example of the Wright Brothers," he said. "They got a plane off the ground. It would be wrong to fault them because it couldn't go to the moon."

Masters and Johnson were disputing charges leveled by a New York journalist, Philip Nobile, and two California psychologists, Bernie Zilbergeld and Michael Evans. Several of the charges were based on "distortion and innuendo," Johnson said, but she and Masters agreed that their evaluation procedures had been flawed--at least by present-day standards.

"We were just two people at a time when a human need was emerging," said Johnson. If they were not as rigorous as possible in monitoring their early clients, she said, it was partly because of a determination not to make the clients themselves think of sex therapy as "work" oriented toward an imposed "goal." Such goals "produce problems rather than satisfaction," she said.

Only a few minutes earlier, Zilbergeld and Nobile had held their own impromptu press conference in an adjoining room, where they repeated criticisms aired more than two years ago in Psychology Today magazine and elaborated on in the current issue of Forum.

Zilbergeld, saying he had been described as both the "Joe McCarthy" and the "Ralph Nader" of the sex-therapy world, acknowledged that brief sex therapy was "a great step forward" in treating simple sexual problems. But he attacked the criteria used by Masters and Johnson in evaluating their results, and he attacked their failure to state those criteria in the text of "Human Sexual Inadequacy."

"We had to write the book in seven weeks," Masters countered. "We put all the statistics on results in there. We forgot--we literally forgot--to include the criteria." He said he had apologized "hundreds of times" for that failure over the years, and "I don't know what more I can do."

In fact, it was only at yesterday's session of the sexologists' congress that Masters and Johnson first offered a written presentation of the evaluation criteria used to determine pre-1969 rates of "failure" and "non-failure" at their world-famous institute in St. Louis. (They had not used the word "success" because, as Johnson explained yesterday, "we believed, and we still believe, that we know more about failure than we do about success.")

In 1958, when the criteria were formulated, sexual dysfunctions were poorly understood and there was no established standard for judging the results of therapy, Masters and Johnson said. So they decided to rate results "in relation to client goals." Just the same, "therapeutic outcome was judged on what was regarded as a conservative basis."

In the Forum article, Zilbergeld refers to the Masters and Johnson data as "not organized, not specific, nothing that we would call rigorous or scientific." He also reports being told by Masters recently that an anorgasmic woman might be classified a "non-failure" if she had just one orgasm during her two-week therapy at the Masters and Johnson Institute, and just one more during the next five years. "Given what Dr. Masters told me in San Francisco, the success rates reported in 'Human Sexual Inadequacy' are certainly misleading," says Zilbergeld. "It suggests to me that Masters and Johnson got carried away with their own enthusiasm."

Masters said yesterday he had been misunderstood, although perhaps not literally misquoted, by Zilbergeld. While he may have told Zilbergeld that such a thing could happen, it was a purely theoretical statement, Masters insisted. He had been thinking about the possibility that a woman might become a widow soon after treatment and have only two sexual encounters in the five years after therapy. In any case, Masters said, no such woman existed in the annals of his institute.

He also said he had not been speaking for the record during his discussion with Zilbergeld. It was only a "meeting among quote-unquote professionals," he said. "We were sitting down as professionals and chewing on something."

After the Masters and Johnson press conference, Masters passed Zilbergeld in the crowded corridor, thanked the reporters for their attention and swept on by.

"He doesn't even say hello anymore," said Zilbergeld.