WE'LL BELIEVE IT when we see it, but more and more senators today seem to be agreeing that after 170 years of efforts - including the introduction of more than 150 joint resolutions and the holding of some 25 different sets of hearings on the subject - it may just be time to approve full representation in Congress for the District of Columbia. That is precisely what more than two-thirds of the House of Representatives concluded about three months ago; and so far, bipartisan support in the Senate has been encouraging. By and large, the arguments still voiced bydiehard opponents have paled in the face of constitutional scholars's testimony on the issue, not to mention a prevailing sense of what is just.

It is dilatory (and silly) to argue, for example, that if the people of the District need representation they should become part of Maryland; there is absolutely no evidence that Maryland wants to absorb the District. Similarly, those who fear that the move for D.C. representation will somehow set a precedent for big cities such as New York to seek separate recognition in the House and Senate can rest easy: At last count, the people of those cities - by virtue of living in a state, as well - seemed to have their own full-fledge emissaries in Congress already. Moreover, we're talking about a District of Columbia, not a city within a state.

But we needn't repeat all the old familiar arguments here. They're being made, and made well, by an increasing number of people in the 50 states, as well as by editorials around the country, and a citizen effort is being made coordinated by members of Congress, leaders of both political parties, the Self-Determination for D.C. coalition and the local Common Cause office. Especially impressive is the list of names attached to a recent letter urging each senator to vote for the representation resolution when it comes to the floor. Supporters include Republican National Committee Chairman William E. Brock; Democratic National Committee Chairman John C. White; Paul Hays, chairman of the D.C. Republican Committee; Robert B. Washington, chairman of the D.C. Democratic State Committee; the mayor, the D.C. Council chairman, and the presidents of the Metropolitan Washington Board of Trade, the D.C. League of Women Voters, the D.C. Chamber of Commerce and two bar associations.

We trust the bipartisan leadership of the Senate senses this growing support for D.C. representation - both downtown and on Capitol Hill - and will react accordingly by scheduling a vote early this summer.