IF THE SUPREME Court really wants to cut its workload, it has a chance to do so in a major case this session. The case involves the redistricting of New Jersey's congressional seats, and it gives the court a chance to set forth a rule that will clear up a lot of uncertainties for politicians and their constituents and lighten the workloads of a lot of courts.

The New Jersey case arises because Republicans didn't like the job the Democrats did of redrawing the district lines in the final days of Democratic Gov. Brendan Byrne's term in office. So they went to federal court and got two of three judges to throw out the legislature's plan, on the grounds that other plans before it--including one mailed to all members of the New Jersey legislature by a Prof. Reock --had smaller differences in population between the districts. The grounds for the decision seem flimsy: the maximum difference between district populations was only 0.6984 percent--considerably less than the 1 percent statistical margin of error in the census figures that are used in all redistricting plans. In a very precise statistical sense, there is no difference between the plan the legislature passed and the one two judges said it should have passed instead.

This case gives the court a chance to set down explicitly a rule it has already hinted it would like to follow. All districting plans should be approved if the population differences in them are less than the statistical margin of error in the census. No other factors should be taken into account, except for the requirements of the Voting Rights Act and the Constitution that require fair representation of racial minorities.

For courts, such a rule has the considerable advantage of being easy to apply. Any judge who can do arithmetic can decide whether to invalidate or uphold a plan in about five minutes. The ease with which such decisions can be made will in turn discourage litigation, since the possibilities for delay and mischief will be vastly reduced.

But, some will say, what about gerrymandering? Shouldn't the Supreme Court leave the federal courts some leeway to overturn plans that give a party or faction great advantage? The answer is that strict implementation of an equal population rule, limiting the difference in size of districts to the 1 percent margin of error in the census, already imposes a tight constraint on any redistricters. Yes, they can take some advantage. But over a 10-year period, in a nation of fluctuating opinions and a politics where candidates' personal appeal often overcomes partisan preference, such advantage is inevitably marginal and temporary. In the past, some justices wanted to give legislatures leeway to exceed the population limits in order to seek other goals, and before the Supreme Court established the one-person-one-vote doctrine, such an approach kept the courts from interfering with the process. But now the best way for the Supreme Court to minimize judicial interloping in the political thicket is to make it clear that it will enforce a hard-and- fast population rule and the Voting Rights Act-- and nothing else.

Last year the court recognized the legitimacy of politically motivated redistricting when it said a court, in the absence of a finding of a violation of the Constitution or the Voting Rights Act, could not "disregard the political program" of the Texas legislature. Now the court has given itself the chance to keep judges from interfering with what it called in 1973 "inevitably political decisions," whether made by New Jersey Democrats or Indiana Republicans. This is the Supreme Court's chance to keep the courts out of such political thickets for good.