JUST WHEN THINGS started looking right for Senate approval of full congressional representation for the District, there comes word that a tiny band of misguided Republican senators is using "Senate procedures" - that's code for a filibuster threat - to prevent a floor vote. The leader of this move is Sen. James McClure of Idaho, whose cockeyed thinking on this subject is nicely defined by his proposal to return the District to Maryland.

Sen. Orrin Hatch of Utah and Dewey F. Bartlett of Oklahoma are pedding comparable claptrap. The others who reportedly have refused so far to agree to a time limitation on debate are Paul Laxalt of Nevada, Clifford L. Hansen of Wyoming and - wouldn't you know - William L. Scott of Virginia, world traveler and perennial exponent of prehistoric attitudes.

Oh, we must't forget to mention another of Sen. McClure's contributions to enlightened thinking on this subject: When the amendment proposal reaches the Senate floor, he says, he 'll introduce a refinement that would grant congressional representation to all cities with populations equal to or greater than that of the District - without regard to the fact that the people who live in those cities already have full representation in Congress. It is almost embarrassing to add at this point that Sen. McClure's home state of Idaho, in its entirety - and never mind its big cities - is smaller in population than the District of Columbia.

So there you have the quality of the hard core of opposition to congressional representation for the District - which, when you consider that constitutional scholars have found no reason to deny full seating - boils down to votes against the people of the District and the kinds of residents they would elect to represent them. That, to be blunt about it, is a civil-right issue, one that should be a matter of party integrity for Republicans as well as Democrats. It is also a matter of political interest to such Republicans as Strom Thurmond of South Carolina, who is up for reelection, and Bill Brock of Tennessee - who has sought to improve the reputation of the party among black voters. Their ability to deliver a successful floor vote on this proposal will surely be watched by concerned voters not just in their home states, but across the nation.

Senate Majority Leader Robert C. Byrd of West Virginia should not let the threat of a sideshow by six senators block consideration of the proposal. If it takes a cloture vote to stop a 1978 civil-rights filibuster, so be it; it will take two-thirds of the Senate to approve the proposal anyway. To let the matter die now at this point - after two-thirds of the House has given approval to the approval - would be a cruel blow to all who have fought so long and hard to end the tyranny of taxation without representation in the capital of the nation.