This year, the traditional configuration of power in Washington -- December fund-raisers for the November victors, orchestrated "grass- roots" lobbying, the overpowering of the nation's main streets by Washington's K street -- has a new element: the prospect of a realignment of the voters. The United States is at a moment in history when specific policies on taxation, spending, race relations and arms control are going to be determined as much -- if not more -- by considerations of the partisan balance of power as by special interests.

The prospect of using legislative and policy initiatives to force realignment is most apparent in the Reagan administration's decision to adopt tx simplification as a cornerstone of its agenda for the 99th Congress. The legislation, a virtual 180-degree turnaround from the business provisions of the administration's 1981 tax bill, seeks to address what many political analysts believe to be the core weakness of the Republican Party: the public perception of the GOP as the party of the corporate rich.

From an electoral point of view, the tax debate is a straightforward gamble. The potential gains to be made in the middle class as a result of a politically successful tax simplification initiative far outweigh potential losses among the affluent.

Suppose, for example, that there are 100 million voters in 1988. If enactment of a substantive change in the tax system increases GOP partisan identification by 4 percentage points among middle-class voters -- those making between $20,000 and $50,000 -- but also causes a 10 percentage- point defection among those making over $50,000, the Republican Party comes out a winner. There would be a net gain of 4.24 million among the far more numerous middle-class voters, against a loss of 2.6 million among the well-to-do, even given the unlikely assumption that 10 percent of the rich coupon clippers angered over the loss of their tax shelters would vote Democratic.

At least two other factors are working to encourage Reagan administration support of tax reform legislation.

The first is the declining political and economic strength of the tax-sensitive independent oil industry, which in 1980 was a critical source of major donor contributions to the Republican National Committee and to conservative Republican House and Senate candidates.

The second is the collapse of the united front of the business community. Firmly behind the corporate tax cuts in the 1981 tax bill, the business lobbying community is now fragmented by competing tax priorities: reduction in the top rate, depreciation schedules, capital gains and research credits -- a split making tax simplification politically possible.

But enactment of tax simplification legislation still promises to be an extraordinarily wrenching experience for the Republican Party. At one level it will be a struggle between architects of realignment, and a network of corporations and trade associations with plants and facilities in every congressional district in the country.

The strength of the prospect of realignment as a legislative and policy-making force has emerged on at least two other fronts where the Reagan administration is working to reduce Republican political liabilities. The Strategic Defense Initiative, or "Star Wars," represents one of the most radical and innovative attempts to use a legislative proposal to fundamentally change the terms of the political debate. Whether or not Stars Wars is militarily feasible, the initiative is a masterful political public relations gambit, suggesting that the Republican Party has the means to allow the United States to escape the nightmare of mutual assured destruction.

Similarly, the Reagan administration and conservative allies are using a twofold strategy to add blacks to the GOP rolls, and to win the loyalty of a larger number of white voters raised in an era of liberalized race relations. The first half of the strategy is an attempt to discredit traditional civil rights leaders, painting them as the principal beneficiaries of liberal spending programs that have encouraged welfare dependency among the poor.

The second has been to encourage the emergence of blacks sympathetic to the administration through grants from conservative foundations and special White House meetings. It is an attempt to establish a black beachhead for the GOP based on class and economic interest.

A strength of the Republican Party lies in the potentially productive tension between its own constituent interests: corporate supporters versus younger political strategists, traditionalists concerned with the deficit versus supply-siders, Christian fundamentalists versus those seeking the votes of more libertarian urban and suburban voters. Whether this tension will produce a vision of society that can lead to and sustain a real realignment after Reagan leaves office remains to be seen.

What is clear is that the Democratic Party is having enormous difficulty on all fronts. In the case of tax simplification, the Reagan administration has effectively taken over center stage with legislation that owes its parentage to a concept first put forth by two Democrats, Sen. Bill Bradley of New Jersey and Rep. Richard Gephardt of Missouri. The GOP's difficulties with its affluent contributors who benefit from existing tax exemptions pale beside those of the Democrats, who are proportionately more dependent on big donors in the tax-sensitive real estate and capital-intensive manufacturing industries.

On military spending and arms control, Democrats remain so fearful of reviving the party's anti-Pentagon image of the 1970s, and so divided on the moral and technical aspects of military power, that they have not yet as a party formulated a coherent stance on defense issues. And the Democratic Party has yet to balance the deep loyalty of black voters and the tensions that minority rights have caused among almost all white constituencies.

Conflict for the Democrats has not, in recent years, been productive; as one Democratic strategist puts it, "we defy physics, we are smaller than the sum of our parts." For the Democratic Party, this is a very dangerous position in a struggle to regain the allegiance of a fluid electorate at a time when the federal government is administered by a party increasingly committed to both a redefinition of national responsibilities, and a realignment of the partisan allegiance of the electorate.