JOHN ANDERSON, the once and future independent presidential candidate, had it almost exactly right, although maybe not for the right reasons, when he hailed the victory he won in the Supreme Court Tuesday as a "landmark decision." It was a landmark all right--not because the court broke new ground, but because it staked out some familiar territory a little more clearly than it had before.

At issue was an Ohio law requiring independent candidates for president in 1980 to file petitions with some 14,500 signatures by March 20 in order to get on the November ballot. This law posed problems for Mr. Anderson, who started off seeking the Republican presidential nomination and did not announce his candidacy as an independent until April 24. So he sued to get on the ballot, and, although he lost in U.S. District Court, the decision was stayed on appeal, and Mr. Anderson appeared on the ballot in Ohio, winning 6 percent of its votes.

Naturally, Mr. Anderson is pleased: his campaign spent more than $1 million on ballot access cases in 1980. It is not clear, however, why its legal fees were so high; George Wallace, running in 1968, got on the ballots in 50 states in a much less favorable legal environment without spending anything like that amount on fancy law firms. And in 1984 the main beneficiaries of this rule, if any, will not be Mr. Anderson, who has plenty of time to qualify for state ballots, but potentially competitive independent candidates who decide to run at what is, in our ever lengthier presidential campaigns, the last minute.

Still, the principle behind the court's decision makes sense: the state's interest in keeping relatively late-filing candidates off the ballot is petty compared with the voters' interest in having candidates with genuine support listed. This is in line with the general trend in election law striking down any laws limiting access to the ballot--by candidates or voters--except those necessary for the orderly functioning of the election process. Thus states as a practical matter can't impose more than a 30-day residency requirement on voters in presidential elections.

Some may argue that the states should be able to make access to the ballot difficult for third parties and independents in order to strengthen the two-party system. But the court's decision explicitly allows states to require substantial numbers of signatures to be filed before such parties or candidates can be listed; you can be asked to show some evidence of wide support before you can get on a ballot. In the long run, the two major parties cannot be protected from all competition, and the existence of such competition may make them stronger. We can trust the voters to distinguish between frivolous and serious candidates; they've never elected the man in the Uncle Sam suit to anything. Fifteen years ago the court overturned another Ohio law, one that kept George Wallace off its ballot; in that case and in this it was wise to view with suspicion laws that minimize rather than maximize the voters' choice.