THE NATIONAL Rifle Association has found a new, and rather fascinating, test for would-be judges. It has announced that Rep. Abner J. Mikva (D-III.) is "unfit" to serve on the U.S. Court of Appeals here because he has been an outspoken advocate of gun-control legislation.

While no one, except mayby the NRA itself, takes its opposition to Rep. Mikva's nomination seriously, the basis for its objection presents all sorts of interesting possibilities. Obviously, if one person is unfit too be a judge because he has staunchly supported gun control legislation, everyone who has opposed it is also unit. And the same, we suppose, could be said for those who have stated firm views on obortion, prayer in the schools, the Equal Rights Amendment or any other controversial issue.

If such a test were to be applied universally to the federal judiciary, remarkable changes would occur quickly. Almost every politician would be eliminated for consideration; most of them have been forced at some point or other in their careers to become staunch advocates of something or other. Lobbyists, of course, would be disqualified automatically. So would everyone else who has had much of a role in public life.

Pretty soon, as you proceed down the list seeking judicial candidates who have never stated a firm opinion on any controversy, al that would be left to choose from would be the most recent graduates of the law schools. Even some of them would be ruled out.

Of course, the nation could begin to breed a class of judges. They could be elected in early childhood, trained to make decisions a Little League umpires, and shielded from the pressing questions of our time. That might not do much for the judiciary, whose members need to know something about the real world as well as legal theory. But it might do wonders for the quality of the umpires.