While the Reagan administration is working to relax affirmative-action requirements, a study by the Labor Department has found federal affirmative-action requirements extremely effective in bringing blacks, women and Hispanics into the work force.

The study has not been published. And some congressional sources believe that there have been attempts to suppress it.

The administration strongly opposesaffirmative-action numerical hiring goals that have been in effect for more than a decade for federal contractors. Assistant Attorney General William Bradford Reynolds, who heads the civil rights division, has called affirmative-action quotas the equivalent of a "racial spoils system" and made it clear that he will oppose them in court.

A draft of the study, obtained by The Washington Post, said that companies doing business with the federal government and, thus, subject to special affirmative-action requirements, "have posted significantly greater gains in the employment and advancement of minorities and women" than companies with no such obligations.

Under federal law, all companies are prohibited from discriminating on the basis of gender, race or national origin. But those with federal contracts worth $10,000 or more must take affirmative action, subject to federal review, to hire women and members of minority groups in proportion to their representation in the work force. The administration is considering seeking a change in that law.

The Labor study, which examined hiring practices at 77,098 businesses between 1974 and 1980, found that minority employment grew 20.1 percent at companies covered by affirmative-action requirements but by only 12.3 percent at companies with no government business and no special hiring requirements.

During that time period, employment of women grew 15.2 percent at companies with affirmative-action programs, compared to only 2.2 percent at the other companies, the study said.

Before affirmative action, the study said, "Where minorities were employed, they were found almost entirely in the so-called '3H' jobs--hard, hot and heavy. Women were concentrated in clerical occupations in business and industry in general, and in low-paying, semi-skilled jobs in women-intensive industries, such as garment manufacturing and food processing."

The study found that affirmative action also helped women and minorities move into management.

For example, the study found that at businesses with affirmative-action programs, the number of black "officials and managers" increased 96 percent. The number of women in that category rose 73 percent, compared with 6 percent for white men.

In companies without an affirmative action program, the number of blacks and women in those high-level jobs also increased but not as much. Those companies showed a 50 percent increase for blacks, 36 percent for women and 7 percent for white males.

The study was requested in 1981 by Ellen Shong, director of the Office of Federal Contract Compliance Programs, and was conducted by J. Griffin Crump. Neither could be reached for comment.

Another unpublished report, just completed for the Labor Department by Jonathan S. Leonard of the University of California, has similar conclusions. It found that as affirmative action has increased the demand for minority workers "it has increased their earnings as well as their employment and occupational status."