The Republican gains in the House and their takeover of the Senate will mean drastic changes next year in the lineup of the two committees that look over the shoulders of federal workers, hand out their legislative goodies and advise congressional colleagues on what should be done with the bureaucracy.

On the Senate side, there will be a new chairman (the first Republican in 26 years) for the Government Affairs Committee. The committee would serve as the pipeline for any reorganization plans President-elect Reagan proposes. a

Sen. William V. Roth Jr. (R-Del.) is likely to wind up heading the committee. He now ranks number three on the minority side, after Sen. Jacob K. Javits, who lost his New York race, and Charles H. Percy of Illinois. But Percy will probably become chairman of the prestigious Foreign Relations Committee.

Roth considers himself a reformer. He cosponsored open-government and sunset" legislation that would require regular justify-your-existence-reviews of federal operations. Roth's family lives in Wilmington (his wife is a practicing lawyer) and his commutes weekends. Insiders say he is unlikely to embark on any early crusades -- they expect the committee will be busy with reorganizations plans and confirmation of Reagan appointees -- if and when he takes over as committee chairman.

The number of two majority seat on the 1981 committee may go to Sen. Ted Stevens (R-Aalaska), one of the staunchest supporters feds have in Congress. The pipe-smoking, independent senator fought hard against the Carter Administration plan to abolish one of the two cost-of-living raises that U.S. retirees get each year. Also moving up -- this time as a majority member -- will be Maryland's popular Sen. Charles McC. Mathias Jr. He is one of the few Republicans in Congress that got endorsements and help from federal and postal unions.

Ranking minority members in the new committee will be defense-advocate Henry M. Jackson (D-Wash.) and Thomas Eagleton (D-Mo.). If the Democrats had kept control of the Senate, Eagleton, who is anxious to trim fat from federal pension systems, would have been the next chairman.

The chairmanship of any committee is important. The personality, interests and work habits of a chairman -- whether he is weak or strong, bored or dedicated -- make a lot of difference. Retiring committee chairman Abraham Ribicoff (D-Conn.) was less interested in the civil service-side: of the committee than many of his predecessors. For example, Ribicoff made it known that he would not push union-favored legislation to liberalize the Hatch (no politics) Act. Because of that, the Senate failed to act on Hatch Act changes, although the House sent them over twice by overwhelming votes of approval.

Although Democrats will control the House next year, their margin has been reduced. It will change the face of the Post Office-Civil Service Committee. If Rep. William Ford (D-Mich.) takes another post, chairmanship of the committee will pass to Rep. William Clay (D-Mo.).

Clay was a popular give-'em-hell speaker at federal union conventions last year. He urged federal workers to get political, to reward friends and punish enemies. Clay said there was little difference between Carter and Reagan.

A one-time business agent for the American Federation of State, County and Municipal Employees, Clay would be the only black committee chairman in Congress.

Two of federal workers' best friends -- Virginia Democrats Herbert Harris and Joseph Fisher -- were upset in the election. They, along with another defeated candidate, Rep. Robert Bauman (R-Md.), helped persuade the House not to cut back the number of cost-of-living raises for government and military retirees. Fisher and Harris represented -- very well -- districts with large number of federal workers. Harris was chairman of an important subcommittee, and helped fight government contracting-out. Fisher was not on the committee, a fact that challenger Frank Wolf used against him. Wolf says he will get a seat on the Post Office-Civil Service panel and he expects to be an important link with his federal constituents and the new Republican administration.