Nat Hentoff complains that 18,000 out of New York City 345,000 arrests are thrown out because prosecutors decline to bring a case to court [op-ed, Sept. 4]. That sounds like a reasonable percentage for police who are doing their jobs. Knowing that cases can be thrown out for technical defects in the evidence, it isn't surprising that about one in 20 arrests result in a summary dismissal of charges. But there is a big difference between an arrested person who is found not prosecutable and one who is innocent.

If the police are conscientious and professional, it's probable that in 90 percent of the criminal arrests with insufficient evidence, they nonetheless arrested the guilty parties. Far from Mr. Hentoff's assertion that the one out of 20 arrests involved innocent people, what actually takes place is the "Scottish Verdict" -- it is not proven. The police know their business, but in a number of cases there will be defects in the evidence or records that preclude prosecution on purely technical grounds. Further, any competent defense counsel will confirm what security professionals know -- that only a minuscule proportion of those charged with violent felonies are innocent of the charges.

Notwithstanding that 5 percent of the arrests do not result in prosecution, most people probably would prefer aggressive policing in order to enjoy the livable city that has resulted rather than to return to the societal anarchy when the thugs ruled. While all of us should cherish the Fourth Amendment protections against unreasonable search and seizure and the guarantees that citizens be safe and secure in their own homes, it is perverse to compare the complaints of the citizen farmers and townspeople who threw off British military occupation to the inconveniences suffered by wrongdoers who are overwhelmingly guilty of what they are charged with. That type of thinking helped to destroy the cities of this country in the second half of this century.

ROBERT M. LEVINE

Malvern, Pa.