AS AN EXAMPLE of the enormous changes that Tuesday's vote promises for American politics, consider the case of the Senate Labor and Human Resources Committee. This committee has been for many years the foremost promoter and defender of liberal causes in the Senate. No more. The defeat of two important members -- Sens. Gaylord Nelson and Jacob Javits -- the prospective change of party control from Democrats to Republicans, and the Abscam indictment of Sen. Harrison Williams, the committee's present and longtime chairman, signal a dramatic change in both the character and the probable role of the committee. It is instructive to note, however, that this is more of a finishing touch to a process long since under way than a sudden development, and that process mirrors a larger trend in American thinking about social programs generally.

There was a time when the cream of the Senate Democratic crop fought for a seat on the Labor and Human Resources Committee. It was, after all, the committee of the Great Society. Under the leadership of its Democratic chairman, Sen. Williams, and its ranking minority member, Sen. Javits, the committee drafted and frequently initiated the huge amount of expansionary social legislation establishing a federal role in almost every area of domestic concern from labor policy to alcoholism control and nutrition programs for the elderly.

Legislation written by the committee turned federal health research into a large-scale enterprise, revolutionized the care of the mentally retarded and established a major federal commitment to education. The committee legislated the principal "War on Poverty" programs -- VISTA, the Job Corps and Legal Services -- and saved them from extinction by President Nixon. In the labor field, it wrote legislation regulating occupational safety and health, assisting miners with black lung disease, setting minimum standards for private pensions, increasing the minimum wage to keep pace with inflation and establishing a multi-billion-dollar employment and training program for disadvantaged and dislocated workers.

But these things began to go out of political and economic vogue. And by the time of the 1976 elections the committee's heyday was over. The caucuses then organizing the Senate found few new senators interested in joining this bastion of liberalism. Even some former big spenders preferred the opportunity to demonstrate their fiscal conservatism afforded by such committees as Budget and Finance. Still, the committee was not without power and influence, occasionally irritating the rest of the membership by forcing votes on unpopular issues.

The prospective ascendancy of Sen. Orrin Hatch of Utah to the chairmanship will surely give the committee a sharply different cast at least in matters of labor policy, even though Sen. Hatch insists he sees no reason to be "confrontational" with the unions in his new job. And for incoming Republican senators, the opportunity to join up and slash major domestic spending programs may have its attractions. But the interesting question is whether they will conclude that assuming close personal responsibility for big cuts in specific local health, education and employment programs is such a good platform after all from which to appeal to voters back home six years hence. And here you reach a key question hanging over the entire new Republican adventure. Will ideology and conviction yield to the necessities and blandishments of elective politics? How will it work? After two decades, a major force for social change -- the Senate Labor and Human Resources Committee -- has disappeared from the American political scene. But politics hasn't disappeared from the American political scene. Stay tuned.