Challenging an important axiom of the women's movement, two California economists reported today that the wage gap between men and women is narrowing rapidly and has not remained constant for the past half-century as widely believed.

The 96-page report by Rand Corp. economists James P. Smith and Michael P. Ward said that women's pay as a percentage of men's was far lower in the 1920s than previously reported but has jumped from 60 to 64 percent in the last four years -- the "largest and swiftest" gain of the century.

By 2000, they said, women's pay will have risen to "at least 74 percent" of men's if present trends continue.

The economists attributed the gains to women's improving education and work experience "rather than legislation, government commissions, or political movements."

Their conclusions instantly added fuel to the debate over "comparable worth" -- efforts to legislate standards of comparable pay for comparable jobs held by men and women. These efforts have become an issue in the political campaign, with women's groups and Democrats generally in favor of them and Republicans against.

A rapidly closing wage gap "would be wonderful if in fact it happens," said Judy Goldsmith, president of the National Organization for Women. "But it would be nothing but naive to say that the advances in women's education and work experience had nothing to do with legislation or political pressure."

Diana Rock, head of women's rights programs for the American Federation of State, County and Municipal Employes, said the report was contradicted by several other studies showing a static or even widening wage gap in some areas.

Smith, who along with Ward received his doctorate in economics from the University of Chicago, said "the male-female wage gap is real, and some part of the disparity is undoubtedly due to discrimination. Our report does not address that issue, but it does suggest that the gap is narrowing and is not as immutable as it appears."

He said he anticipated criticism from women's movement activists. "There is a tendency, when you have a suggested remedy like comparable worth, to be distressed when you have something that shows progress" without the remedy, he said.

The report said government figures showing women's wages stuck at about 59 percent of men's wages for the last several decades suggest "an inflexible labor market that has failed to reward the obviously increasing skill of women as more of them have entered the labor market and more have stayed in it . . . . Such pessimism is one reason that some have called for a massive governmental and judicial intervention into American labor markets in order to eradicate wage disparities between the sexes."

The 59-percent level, the report concluded, "is a myth," an average kept artifically low over the decades by a continuing large influx of female job-seekers with less education and experience and lower wages than the typical working woman. Even that average, he said, has begun to jump significantly.

Government statistics compare only working women to working men, which "seriously distorts the actual trends in the economic status of all women relative to all men," the report said. By analyzing "skill distributions" for female workers and for women overall, Smith said he and Ward were able to show that individual working women -- apart from the averages -- are catching up to men.

Their analysis shows that pay for all women as a percentage of men's pay was much lower in previous decades than has been reported -- 43 percent in 1920, 48 percent in 1950 and 53 percent in 1980. But the figures show that women's wages grew 20 percent faster than men's wages in those 60 years.

Cathie Shattuck, a GOP attorney here and a former vice chairman of the Equal Employment Opportunity Commission, called the study "pretty accurate" and said it tends to show that "if women have a chance to compete, they will do so, and comparable worth is not needed."

Goldsmith sharply disagreed. She said the women's gains reflected in the report arose from new opportunities in education and the work place forced through federal legislation, the same legislation that she said is now threatened by adverse court decisions and lax Reagan administration enforcement.