One of the unexpected, but fortunate, side effects of the presidential race is that it has focused attention on the way the politicians have rigged the ballot against third parties.

No other democratic country makes it so difficult for a new national party to emerge. In the United States, only the two major parties have automatic access to the ballot: all the others must overcome a 50-state obstacle course.

This has been going on for a long time, but it has attrached only passing notice. Now, however, there has been a surprising burst of interest, undoubtedly aroused by the independent appeal of Rep. John Anderson. Unlike most such movements, this one is being taken seriously, for it could in various ways be a telling factor in the November election.

It is of course, too late for any reform this year on the anti-third party rules, but they surely will get some attention in the next Congress, which will be confronted with growing demands for a general overhaul of the U.S. electoral system.

Every presidential election inspires fresh interest in such sorely needed reforms. Hopes were momentarily raised by Jimmy Carter in March 1977 when, in a special message to Congress, he proposed sweeping voting changes at both federal and state levels. He called for a constitutional amendment to abolish the Electoral College in favor of electing the president by a simple majority of the popular vote. He also proposed elimination of restrictive state laws on registration and endorsed federal campaign funds for congressional candidates.

Howard Baker, the Senate Republican leader, no only endorsed the easy-registration idea, but proposed broadening the legislation by making Election Day a national holiday, along with keeping the polls open for 24 hours. John Rhodes, the House minority leader, predicted the legislation would pass "with a lot of Republican support, including my own."

Alas, it was not to be. When the Republicans began having second thoughts, Carter, no longer assured of an easy success, turned his attention elsewhere, and so the changes have remained in limbo; not forgotten, but waiting for a more propitious moment -- like early 1981 -- when there will also be a flock of new bills to reform the man-killing primary system.

Meanwhile, it is not likely that the problem of getting on the ballot -- Difficult as it is -- will keep John Anderson from running as a third party candidate, for, as George Wallace proved, the obstacles can be overcome by a determined, nationally organized effort. Few doubt that Anderson, with his demonstrated appeal to independents as well as dissidents of the major parties, would run stronger than Wallace, and could well force the election from the Electoral College to the House.

What the House might do staggers the imagination. First, the decision would be made not by the present Democratic-controlled House, but by the one to be elected in November, composition unknown. By a quirk of the Constitution, the next president could be elected by a minority of the House, for each state has just one vote, determined by a majority of each state's delegation. The rub is that the five largest states (with over 70 million people and 154 congressmen) would have no more say than the five smallest states (1.7 million people and five congressmen).

One of the little known peculiarities of the Constitution is that a candidate, to be elected by the House, must get an absolute majority of the states. The Constitution anticipated this might produce a prolonged deadlock, in which event the Senate is empowered to elect by majority vote an acting president -- but it is limited to choosing between the two candidates who got the greatest electroal vote for vice president. It sounds more like Rube Goldberg than the Founding Fathers, but that's the loony way it is.