A new study by the General Accounting Office says that women working for the federal government make 63 percent as much as their male colleagues, primarily because they are concentrated in low-paying clerical jobs and lack seniority.

The GAO study, based on 1980 census data, says women in the private sector are paid 56 percent as much as men. In state and local governments, women's salaries are about 71 percent of men's, according to the study.

GAO's report is background data prepared for Congress to use when it takes up the politically explosive issue of pay equity. Legislators want to determine if the pay gap is the result of sex discrimination in the pay and job classification system.

If so, Congress could recommend legislation or guidelines to determine how pay equity could be established between dissimilar jobs that may require equal levels of training, education and responsibility.

The issue is political dynamite.

Backers of the study note that women, who make up less than 40 percent of the federal work force, hold about 90 percent of all jobs in the six lowest pay grades. They say those jobs have been systematically ignored or underrated when pay and grade levels are studied.

Opponents warn that the study could lead to the government setting wage levels for virtually every employer in the nation -- except Congress -- without regard to union agreements or the demands of the marketplace.

Last summer the two sides agreed to postpone the pay equity fight, which was blocking work on other legislation until this year. The Senate Governmental Affairs Committee and the House Post Office-Civil Service Committee have agreed to a study and hearings.

GAO's data shows that white women in government receive 63 percent of the pay that men do, and that black women get 62 percent. In state and local governments, salaries of white women are 72 percent of those for men, and black women get 65 percent of what men receive. In the private sector the figures for white women are 59 percent, and for black women 54 percent.

GAO said the issue is "so complex" that Congress should consider including representatives of all interested parties on the study panel to lay out the issues and options.