Federal affirmative action programs have had no significant long-term impact on the wage gap between black and white males, according to an analysis of U.S. Census data released today.

The report by two economists here also concluded that a brief surge in wages for new black male college and high school graduates dissipated in the 1970s after employers affected by federal civil rights legislation reached their target number of blacks.

James P. Smith, a Rand Corp. economist who wrote the report with Unicon Research Corp. economist Finis R. Welch, said their analysis shows the current debate over modifying affirmative action rules can have little impact on black wages.

"If you're looking for ways to help the average black, it has nothing to do with it," he said.

Instead, the report said, since 1940 the steadily improving education level of black workers has had the greatest impact on closing the wage gap with whites. The analysis suggests that the best way to continue black economic progress, Smith said in an interview, is "to improve the inner-city schools."

The report presents a generally optimistic summary of black economic progress since 1940, noting that annual income in 1984 dollars for the average black male grew from $4,500 in 1940 to almost $19,000 in 1980. That increase was 52 percent more than for the average white male.

But the report notes that black family income, because of the large number of female-headed households, remains far behind white family income.

It concludes that the wage gap narrowed as rapidly in the 20 years before 1960, and before the beginning of affirmative action rules to eliminate discrimination against blacks, as it did in the 20 years after that.

"This suggests that the slowly evolving historical forces (particularly improved education and migration from the rural south to the urban north) were the primary determinants of long-term black economic improvement," the authors say.

The data indicate that affirmative action brought new black college graduates from 75 percent of their white counterparts' wages in 1966 to complete parity in 1972 in the 52 percent of jobs affected by federal legislation.

When those initial targets had been reached, however, competition for black workers slackened and new black graduates were making only 89 percent of white wages by 1976. New black male high school graduates experienced a similar rise and fall in relative wages.