DURING the long debate over wiretapping and suspects' legal rights before questioning, one related issue has been largely overlooked. This is the increasingly routine use of plainclothes policemen in a wide range of areas, including, most recently, the handling of political demonstrations.

In the course of their sometimes-fanatical crusade against marijuana, American lawmen have made the hippie-policemen a standard fixture in many college communities. And in New York last month, this new look in law enforcement moved into politics as hundreds of long haired, shabbily-dressed young policemen overran Columbia in the name of law and order.

The use of plainclothesmen is undoubtedly justified in many situations, especially in combatting organized crime. But this should not hide the fact that disguising the police always has a social cost.

A citizen in a free society has a right to know when he is dealing with a policeman, and when he is not. A Czech liberal noted recently that one of the first signs of democratization in his country was that all the police were wearing uniforms again. Obviously, the use of undercover police in Czechslovakia has been far more oppressive and less restricted than in America. But when a young man is sent to Federal penitentiary for agreeing to sell marijuana to an insistent hippie-policeman, or when a pseudo-member of a Columbia radical group suddenly flashes his badge and arrests the group's leader, it seems clear that the American plainclothesman too, has his repressive uses.

More importantly, the disguising of the police can only serve to create mistrust and suspicion between people. And this cannot be justified solely by the argument that plainclothesman help to catch lawbreakers. Law enforcement must always serve the law itself, and the ultimate purpose of the law should be to promote security and cohesion between all members of society.

The use of disguises in law enforcement cannot help but compromise the very spirit of the law. This should be carefully considered before the use of plainclothesmen becomes so routine that it is no longer even seen as an issue in America.