In 1939, the median income of women who worked year-round was 58 percent of the median income of men. In 1981, despite passage of the Equal Pay Act and an infrastructure, however shaky, of antidiscrimination laws, despite the influx of millions of women into the labor force, that figure has remained essentially unchanged: women now earn 59 percent of the median earnings of men.

These figures, offered in a recent congressional hearing by Dr. Janet L. Norwood, commissioner of the Bureau of Labor Statistics, are at the heart of a subtle but important shift that is taking place in the drive for economic equity for women.

The slogan of choice now is equal pay for work of comparable value, a concept that tackles the historical bias that placed more worth on men's jobs because men were seen as family breadwinners. Jobs requiring strength and endurance were given more value than jobs requiring tact and patience.

One upshot of this value system was that municipal tree trimmers in Denver were paid more than nurses in the city's intensive care unit. Another was that in 1979 a liquor clerk in Montgomery County, with two years' experience and a high school diploma, earned more per year than a school teacher with two years' experience and a college degree. Most of the liquor store clerks were male, while more than two-thirds of the teachers were female.

Labor unions, the Democratic Party and women's organizations are now supporting comparable worth standards as a way of upgrading jobs predominantly held by women. Reps. Patricia Schroeder (D-Colo.), Geraldine Ferraro (D-N.Y.) and Mary Rose Oakar (D-Ohio) recently conducted hearings at which Sens. Edward M. Kennedy (D-Mass.) and Gary Hart (D-Colo.) strongly backed comparable worth as a means of achieving pay equity.

Cautioning that budget cuts and other factors have lowered the quality of available data, Schroeder set forth figures from the Office of Personnel Management that show that women in the federal work force are not much better off than women in the private sector.

As of October 1981, 91 of every 100 blue collar workers in the federal government were men. The typical male blue collar worker earned $20,431, while the typical blue collar woman earned $16,041. Of 1.5 million white collar workers, 46 percent are women. They are concentrated in such traditional jobs as clerical and secretarial, personnel and health fields, which pay an average of 66 percent of the average salary paid in the male-intensive job categories.

The Supreme Court last year opened up the possibility of court suits by women who claim they are paid less for jobs that are comparable to what men are doing. Hart testified that 13 states now have comparable worth language in state equal pay statutes. Others, such as Kennedy, favored including such language in the Equal Pay Act. Kennedy also urged that Congress pressure the Equal Employment Opportunity Commission to issue guidelines on comparable worth for employers.

Clarence Thomas, EEOC chairman, under sharp questioning from Ferraro and Schroeder, said comparable worth issues were an EEOC priority, but he cautioned that class action suits on the issue would be very expensive to his agency. "It's very expensive to the women of this country when the cases are not pursued," countered Ferraro.

While comparable worth is a tricky area, involving subjective judgments and biases about the values of a job's skills, education, duties and responsibilities, the hearings nevertheless showed clearly that women are segregated into frequently undervalued jobs. This is a free-market luxury that society can ill afford when one of every three of the 8 million families headed by women lives in poverty.

The federal government, with 2.8 million employes, is the nation's largest employer, and it has historically taken the lead in doing away with discrimination. The first step toward making comparable worth a standard for the land is public education about what it means. The next logical step is for Congress to commission a study into the way the federal government evaluates its labor force, with the goal of rooting out gender bias and outmoded concepts of worth. The federal government can educate the private sector at the same time it is putting its own house in order.

And it needs to. The federal goverment pays animal health technicians (who are 94 percent male) an average of $19,340. It pays nursing assistants (who are 67 percent female) an average of $13,890. That is neither equitable nor right.