REPUBLICAN NATIONAL CHAIRMAN William Brock and many of his colleagues are keenly aware than, unless their party gains a lot of ground by 1981, redistricting by Democratic legislatures could freeze the GOP out of power in Congress and many states for a decade or more. So Mr. Brock has launched a big grass-roots organizing drive. Far and away the most interesting and controversial (if perhaps will-o'-the-wispish) aspect of this is Mr. Brock's avowed intention of getting more black support for the party. Can it be done? Will it be? Our own provisional conclusion is that there is a larger and better opportunity there than the Republicans are likely to exploit.

For his part, Mr. Brock can cite several 1977 election victories won by Republicans with crucial black support: Virginia Attorney General Marshall Coleman's win with about 30 per cent of the black vote; Rep. Robert Livingston's special-election victory in New Orleans with 30 per cent of the black vote, and the support of 41 per cent of the blacks helped elect the first Republican mayor of Charlotte, N.C. That may not exactly add up to an election tidal wave, but is something - and there is evidence elsewhere that, in theory anyway, the makings exist for a coalition of convenience between Republicans and blackS.

Here and there around the country, for instance, GOP candidates have been courting black workers and homeowners on issues of neighborhood safety and stability, good education and permanent jobs, all subjects on which a certain consensus of views should be possible. Some conservatives have also been seeking alliances in opposition to enviromentalists and advocates of limited growth on the grounds that these are economic stultifiers whose objectives mean fewer jobs for the poor. Former California Gov. Ronald Reagan, in this spirit, was quick to praise the NAACP's criticism of the Carter administration's energy progrzm, which the NAACP has argued would hurt blacks by retarding economic growth. And the Rev. Jesse Jackson, in his recent speech to assembled Republican bigwigs, did carve out some territory concerning both program and values in which Republicans and black voters could live comfortably together - never mind that he also urged some positions that the GOP could never in a million years buy.

The trouble with making very much of all this is that, in the first place, the Repblicans have a history of squandering such opportunity when it comes their way. Incredibly, when the Democratic Party was in its worst throes of racial and regional division and at a time when black political power was coming to mean something nationwide, the Republicans managed to make even the Old South-dominated Democrats look the better alternative to blacks.That was in the early 1960s, and the plain fact is that the GOP gave the Democrats the breathing space necessary to reconstruct themselves on racial questions. Nor has it ever been plain (to understate the case) that the party as a whole, by which we mean the party that convenes every four years to choose national candidates and draft party positions, is even willing to take credit for the racially enlightened programs some of its legislators and state and local officials have helped bring about. It has a way of slighting and/or savaging those Republicans - Sens. Edward Brooke of Massachusetts and Charles Mathias of Maryland, Rep. John Anderson and Gov. Jim Thompson of Illinois - who do preach racial inclusiveness.

The point here is that whatever advantages there are for the GOP in the systematic, large-scale wooing of black voters, such a pitch is seen as being in direct conflict with the party's hopes of picking up disaffected white Democratic voters who are wary of what they regard as the Democrats' liberal permissiveness on racial and other questions. There is certainly some short-term political truth to this. On so-clled "affirmative action" and Bakke -connected questions, for instance, not to mention a whole range of labor and economic-security issues, there would be plenty that would need some very hard negotiation. But that, after all, has been true of the Democrates, too. And the fact is that, as Jesse Jackson and some of the Republica conservatives understand, there is an enormous area of common interest there to be cultivated - if only the GOP had the imagination to do it. Our reluctance to get excited over the prospect proceeds from the unhappy fact that never in contemporary times has the party been able to summon that imagination and sustain it