Senator Obama doesn’t yet have the African-American vote in his pocket, but he’s going all out to steal the feminist vote away from Senator Clinton. He pandered to feminists on Tuesday by endorsing the discredited theory of “comparable worth,” now renamed “pay equity” to make it more appealing.

The occasion was Equal Pay Day — the day of the year, according to the National Committee on Pay Equity, when women’s wages, allegedly only 77% of men’s, “catch up” to what men have earned the year before. The story is that women have to work those extra months to get their fair share.

Never mind that the 77% figure is flawed and bogus. The latest figures show that comparing men and women who work 40 hours weekly yields a wage ratio of 88% — before accounting for different education, jobs, or experience, bringing the wage ratio closer to 95%. Percentages of 88% and 95% are less dramatic — and would place Equal Pay Day in January or February, poor months for outdoor rallies.

According to Mr. Obama, “For too many years, not only have women across America been undercompensated for their hard work, they have been undervalued. Women only earn 77 cents to every dollar that a man makes. Equal work deserves the guarantee of equal pay.”

The Equal Pay Act of 1963 already requires equal pay for equal work, and Walmart employees are suing now under that law.

But Mr. Obama wants still more, and he is a co-sponsor of the Fair Pay Act, proposed by Senator Harkin of Iowa. It calls for equal pay for “equivalent” jobs, whatever that means. Section 3 (a) prohibits employers from paying women in female-dominated occupations salaries different from those paid men in male-dominated occupations, unless “a differential is based on a bona fide factor … such as education, training, or experience. …”

Compared to the Harkin bill, Mrs. Clinton’s Paycheck Fairness Act is restrained. It instructs the secretary of labor to “develop guidelines to enable employers to evaluate job categories.” Employers would not be required to comply with the guidelines, although surely there would be pressure to do so. Onerous as these provisions are, the Fair Pay Act goes further.

Consider a large firm such as Exxon. Would it have to pay clerical workers, mostly women, as much as it pays refinery hands, mostly men? With such “equality,” who would be willing to work at the distant, more dangerous jobs in the refinery?

Mr. Harkin’s bill would require the Equal Employment Opportunity Commission to define male- and female-dominated occupations and review wage reports of firms with more than 25 employees, “including information with respect to the sex, race, and national origin of employees at each wage rate in each classification, position, job title, or other wage group.”

Into how many categories would the commission divide hospital jobs? Bank jobs? Insurance jobs? Would employers with, say, 40 employees split themselves into two companies to escape the paperwork? Wages change constantly and job classifications are imperfect, and can be changed. Employers might not know the race and national origin of workers, and workers might not want to be asked.

For better or for worse, our economic system rewards workers on the basis of how much employers are willing to pay for their service. There is no other measure of a job’s “inherent value.”

And American women are rewarded, although it’s hard to believe from the Equal Pay Day rhetoric. Almost 60% of women work, and the latest unemployment rate for adult women, at 3.4%, is lower than that for men, at 3.5%. Many studies, such as those by Baruch College professor June O’Neill and University of Chicago professor Marianne Bernard, show that when women work at the same jobs as men, with the same accumulated lifetime work experience, they earn essentially the same salary.

Some women are paid less than some men because of the choices they make about field of study, occupation, and time out of the work force for child-raising. Compared to men, women tend to choose more college majors in the lower-paid humanities rather than in the sciences. Men and women who choose computer science and engineering have higher incomes.

Women take time out of the work force to have children and care for them; some choose jobs with more pleasant working conditions, fewer hours, or more flexible schedules. Employees who stop working for a while for any reason miss out on promotions and raises that others get.

Although Congress has not enacted comparable worth, a few states, such as Washington and Minnesota, have done so on state and local government operations. The extra funding for increased women’s salaries comes from the taxpayers and does not cause the governmental entity to go out of business. Requiring private businesses to adopt comparable worth would raise costs of hiring, hurting women’s opportunities.

“Comparable worth” is based on an assumption that women are inferior and weak, chronic victims, and unable to succeed on their own, and so need government wage protection. By supporting Mr. Harkin’s bill, Mr. Obama may get more female votes in Iowa, the first 2008 battleground — but he demonstrates lack of judgment as a presidential candidate.

Ms. Furchtgott-Roth, a former chief economist at the U.S. Department of Labor, is a senior fellow at the Hudson Institute.