The head of the House Civil Service subcommittee believes most government workers should be required to join unions.And he wants the 2.8 million U.S. aides given the right to use their muscle and money to clobber antibureaucratic politicians at election time.

Chairman Bill Clay (D-Mo.) has already steered reform of the Hatch "no-politics" Act through the House. Now, he says he will push for major labor relations changes within the federal government, the nation's biggest single employer.

Clays says he will start off demanding the union shop in government. But he realizes that he may have to settle for an arrangement under which most federal workers would pay union dues - for representation and service - no matter whether they wanted to be members of the union or wanted the representation.

Part of Clay's legislative package would give federal and postal unions greater status and bargaining powers with federal agencies. It also would abolish the present labor-management code was set up - and can be withdrawn anytime - by the President.

Clay believes that his liberalization of the 38-year old Hatch Act will be passed byt he Senate, despite reports that the Governmental Affairs Committee may let the bill die. Clay told an informal gathering of reporters yesterday that he had "reason to believe" that Chairman Abraham Ribicoff (D-Conn.) won't try to block the House-passed Harch Act changes, although Ribicoff personally is cool to the idea.

The Missouri Democrat said that federal and postal workers who get benefits from union contracts and actions should pay for them, even if they don't belong. Currently less than half the federal work force is unionized, and it is illegal to require an employee to join a union to get or hold a federal job.

Clay said the Civil Service Commission has said it might be a year before it studies and comments on a revised labor-management program, and he isn't going to wait a year. He said he might skip CSC input for the moment and push ahead with hearings aimed at getting "some kind" of labor-management bill ready for a House vote by Labor Day.

Clay also took a swipe at colleague Rep. Joseph Fisher (D-Va.) who voted against Hatch Act reform.Fisher, who has one of the largest federal employee voter blocs of any member of Congress, wanted to limit federal and postal employee participation in partisan political campaigns to the state and local level. He finally voted against the Clay version of Hatch Act reform, which most Democrats supported.

Clay, who is black, said he felt Fisher's input from constituents was like a slave-owner of the 1850s polling his slaves on the issue of slavery.

Clay said the "house niggers" who had relatively light duty and good treatment would say slavery was a good thing. Nut the "field niggers" who did the dirty work wouldn't be polled since they would have a different viewpoint, he said. By the same token, Clay said, the Northern Virginia Democrat talked to "supergraders" who have the money and privileges, and not the rank-and-file.

Fisher characterized Clay's comments as "totally inaccurate."

"I conducted a survey of constituents and received replies from over 20,000 of them, many of them members of federal employee unions. The Hatch Act amendments the committee proposed.

"I have consulted personally with federal employees in all grades and in numerous agencies, and have not confined myself to any particular group of federal employees."