In all the focus on President Reagan's struggles with the lame-duck session of Congress and the even tougher time he probably faces with the new Congress that will be sworn in two weeks from now, there has been a tendency to forget the most dramatic change wrought by the 1982 elections.

But two of the newly elected Democratic governors passed through Washington last week, bringing with them a reminder of that change. Eleven of the 36 governorships up in November switched parties. California and New Hampshire went Republican. Nine other states--Alaska, Arkansas, Michigan, Minnesota, Nebraska, Nevada, Ohio, Texas and Wisconsin--switched to the Democrats. In five other states--Alabama, Georgia, Massachussets, New Mexico and New York -- new Democratic governors were chosen to succeed those stepping down.

With the Democrats due to fill 34 of the 50 governorships and to control both houses of the legislature in the same number of states, state government now becomes the major showcase of Democratic Party policy and leadership.

It is an increasingly important level of government. As Ohio Gov.-elect Richard Celeste, one of the recent visitors, noted, the next session of Congress will likely be consumed by the problems of Social Security and the budget. Whatever initiatives are undertaken in other areas of domestic policy will likely be taken at the state level.

Those initiatives will be constrained, of course, by the grim fiscal situation most states face. Wisconsin Gov.-elect Tony Earl, the other visitor, and Celeste both inherit multibillion-dollar deficits from their Republican predecessors, requiring them to raise taxes and trim spending immediately. They know no bail-outs are coming from Washington -- and really are not seeking them.

There is a political irony in the Democratic takeover of state government. More than any of his predecessors, Reagan has been systematically pushing power and responsibility from Washington to the state capitols. Now those capitols are controlled by his political opponents.

The presumption is that the increase in the Democratic strength in the governorships and legislatures will block further efforts by Reagan to hand over programs to the hard-pressed states. Clearly, there will be more resistance to the kind of "federalism" that passes on responsibilities without resources in a time of recession and that takes the deepest budget cuts in federal aid programs. Utah Gov. Scott Matheson (D), chairman of the National Governors Association, said after his first meeting with the newly elected governors that "there's not a single governor" who will allow "federalism and the budget to be separated."

But for the long haul, it would be a mistake to see these new Democratic governors as people who will fight against greater responsibility and flexibility for the states in running domestic programs.

Quite the contrary. My impression is that they will constitute an important power center within the Democratic Party that will force that party to confront, really for the first time, the issues involved in sorting out the powers and responsibilities of national, state and local governments.

The Democrats tend to be a Washington-oriented party, quick to propose national solutions to national problems. For the past few years, the case for a greater state role has been argued by governors such as Matheson, Bruce Babbitt of Arizona, Richard Lamm of Colorado, Jim Hunt of North Carolina and the retiring George Busbee of Georgia.

They were effective advocates, but their southern, western and largely small-state base did not represent the real power center of the Democratic Party. Now they will be joined by people like Celeste and Earl--unusually able, experienced and articulate people. They believe in a positive role for government and want to make their level of government an active agent in dealing with national and even international (trade, technology and resource) problems.

Even before they were inaugurated, Earl joined the congressional debate on the highway bill and Celeste on domestic-content legislation. Along with such others as Mario Cuomo of New York, Jim Blanchard of Michigan, Mark White of Texas and Michael Dukakis of Massachusetts (returning after a four-year absence), they will add a big-state weight to future policy discussions within the Democratic Party and in Washington.

It's a healthy thing for that party and for the future of this country's politics and government.