YOU WATCH "Hill Street Blues." As soon as the suspected extortionist, murderer or cat burglar is caught, the cop grabs him by the shoulder and shouts, "You're under arrest. You have a right to remain silent. Any statement you make may be used as evidence against you. You have a right to an attorney and if you can't afford to hire one, an attorney will be provided." These are Miranda rights, so familiar to most people that if you're watching an old gangster movie and the criminal is arrested, interrogated and denied access to a lawyer, you think, "They can't do that. They didn't read him his rights."

Nineteen years ago, the Supreme Court mandated the reading of this statement to persons being taken into custody in order to protect Fifth Amendment rights against self-incrimination. Before Miranda there was no simple way to distinguish a voluntary confession from an involuntary one. Sure, if it could be shown that a suspect had been tortured, his confession would be invalidated. But suppose he was taken down to the station and questioned by teams of officers for 36 hours straight. Suppose he was moved from one police station to another as his lawyer tried to find him. Suppose he was young and a little slow and the police told him they'd arrest his mother if he didn't confess. These things happened, but by and large they don't any more because suspects know they can talk to a lawyer before making an incriminating statement.

This week, the Supreme Court ruled that it is all right for police to arrest a man, interrogate him, obtain a confession and then read him his Miranda rights and get the confession again. The first confession cannot be admitted in court, but the second can. This may sound reasonable since only the properly obtained confession can be used. But Justice Brennain a furious dissent, explained how this practice really works to circumvent the Miranda rules.

Once the first, inadmissible confession is made, Justice Brennan said, a suspect invariably believes he has "let the cat out of the bag" and he sees no further reason to remain silent or to ask for an attorney. So, the second confession is, in most cases, a direct result of the improperly obtained first one. Unless considerable time has elapsed between the two statements, or the suspect has been advised that his earlier statement cannot be used in court, or he has consulted with a lawyer or with family members between confessions, the second statement should be as tainted as the first, he said.

Justice Brennan is right. Most of today's law enforcement officers have lived with the Miranda rules for their entire careers. A court decision that weakens this established and widely accepted protection can only create uncertainty in the minds of conscientious police officers and put temptation in the path of others. Remember, these rights are read to the guilty and the innocent alike. Everyone has an interest in preserving this vital protection.