When Republicans took control of the Senate, they did more than just replace 12 Democratic senators. They dismantled what had become an important, if seldom noticed, branch of government, the Democratic Senate staff. This is an accomplishment that has vast implications for the practical conduct of government and for the prospects of achieving the reductions in government activity sought by the Reagan administration.

We are not accustomed to thinking of Senate staff members as a separate branch of government, and the Senate staff was not particularly important -- indeed, it scarcely existed -- the last time the Republicans won control of the Senate, in 1952. But today staff is not only numerous -- 6,500 staffers for 100 senators -- but powerful. The staff built up by Senate Democrats -- young, well educated, highly motivated, liberal -- played a critical role in building the kind of big government that the Democrats believed would serve people's interests and that the Republicans believe is wasteful and pernicious.

This liberal Democratic staff grew because senators who wanted an energetic government active in many areas could not by themselves master the details to create and monitor such a government. Staff members advise senators during sessions or at hearings, keep in touch with people in critical positions in the executive branch and create, nurture and perpetuate federal programs that few senators give much thought to. These "submerged horizontal bureaucracies that link the three branches of government," as Sen. Daniel Moynihan calls them, are responsible for many of the programs and policies whose unpopularity or cost helped produce votes for Republicans.

The Republicans understood the power of the staff, and moved quickly once they had the votes to dismantle it. The majority party is entitled to two-thirds of the staff appointments; that meant that as soon as the Republicans took control, half the Democratic staff would be gone. In addition, Republicans such as Strom Thurmond cut the total number of staff positions -- thus reducing further the number of positions for the Democratic minority.

To see what the dismantling of the Democratic staff means, consider the differences between how the Senate handled the incoming Reagan administration and the way the Senate hamstrung the Nixon administration 12 years ago. This time Democratic senators got nowhere in their attempts to raise questions about Cabinet and sub-Cabinet appointees; in 1969, Democratic senators, well briefed by their staffs and allied lobbyists, extracted policy concessions from appointees like Walter Hickel as the price of confirmation. Over the next three years, the Senate almost voted to end a war the administration wanted prosecuted and it defeated major administration projects such as the supersonic transport. It rejected two of the president's Supreme Court nominees.

Staff played a major role in all of these fights, assembling facts and arguments for the senators' positions and helping to frame the issues. A prime example is James Flug, then a staffer for Sen. Edward Kennedy. Flug got the idea into his head that the Supreme Court nomination of Judge G. Harrold Carswell should and could be stopped, and recruited a senator to lead the fight against Carswell. And it was staff who directed the research and raised the arguments that defeated him. This is not said to minimize the role Birch Bayh and other senators played in that fight. But it was a Senate majority -- ably assisted and sometimes guided by staff -- that gave the Nixon administration so much trouble.

Of course, even before the 1980 election, liberal Democrats did not have anything close to a majority in the Senate. By my count, there were no more than 42 dependable liberals. Nonetheless, liberals had much more influence over the actual course of government than their numbers warranted. In program after program, the Senate staffers and agency appointees or high bureaucrats kept programs going that might otherwise have disappeared, and started programs that might otherwise never had existed. There was nothing illegitimate about this; it is not improper to use ingenuity and skill to achieve political ends. But now the staffers and their Rollodexes are gone; the critical phone calls to bureaucrats are not made; hearings are not set up; regulations are not pushed through. The consequences are immeasurable.

The Republicans may have won control of the Senate through luck as much as anything else; they won seven of the nine seats that were decided by less than 2 percent of the vote. Yet luck tends to go to those who are well prepared, and the Republican Party's luck may be transformed, if its policies are successful, into a semi-permanent Republican Senate majority. In 1958, the Democrats picked up 13 Republican Senate seats, in part because they were lucky enough to win most of the close races; for the next 20 years liberal Democrats usually dominated the Senate. Republicans now fill the allotted staff positions, but no one really fills the entrepreneurial role the Senate Democratic staff played in expanding and strengthening government.