For years British police have been warning arrested suspects: "You do not have to say anything unless you wish to do so, but what you say may be given in evidence."

To the Editor: Re "Britain's Civil Liberties Backslide" (editorial, Nov. 28): You are correct in condemning Britain's proposal to warn arrested suspects that not only what they say but their silence as well may be used against them in court.

Carla Del Ponte, the chief prosecutor, said her detectives had produced proof that local government officials regularly warned suspects of an impending arrest, allowing them to escape.

Police no longer need a "Miranda card" to remember how to warn suspects that they have a right to silence and a lawyer.

In those cases, this official said, the Africans accepted arrangements that brought the bureau into interviews from the start or, in some promising cases, at "second phase" interviews where crucial disclosures could be confirmed under the rules that require American investigators to warn suspects against self-incrimination.

Where possible, officers are expected to warn suspects before they shoot.

The Supreme Court agreed today to decide whether the police must warn drunken-driving suspects of their constitutional rights against self-incrimination before asking them questions aimed at testing their mental functioning.

The controversial Miranda rule, under which police must warn suspects that they have a right to remain silent, has been weakened progressively in several Court decisions taken by majorities of at least 6 to 3 and sometimes 7 to 2.

The Miranda rule requiring police to warn suspects of their rights "is always an imposition of initial burden upon law enforcement people, but I am convinced that the burden is an appropriate one.

The study said that while the Supreme Court's Miranda decision holding that the police are required to warn suspects of their rights before questioniong had little detrimental effect on law enforcement, although it "has sparked heated controversy on a political level."