Justice William J. Brennan Jr., joining an unusual public debate among Supreme Court justices, took strong exception yesterday to a colleague's proposal for creation of a new court to select cases for the justices.

Reacting to a speech last month in which Justice John Paul Stevens said the quality of the court's work was suffering because of overwork, Brennan said in his own speech that Stevens' idea would "destroy the role of the Supreme Court as the framers envisaged it" and "sow the seeds of destruction of the court's standing as we know it."

Justice Byron R. White has already criticized Stevens' proposal, in what is fast becoming an extremely visible off-the-bench policy dispute among the justices. Members of the high court ordinarily keep such disagreements to themselves or confine them to opinions and dissents.

Stevens breached that tradition in his Aug. 6 speech to the American Judicature Society, asserting that the court had failed to deal with the caseload problem internally.

The court, Stevens said, was making judgments too quickly in many cases and prematurely in others and, because it was trying to do too much, was relegating important elements of its work to "second class" status for handling by clerks.

Stevens then suggested relinquishing to a new court the authority to screen the 4,000 petitions it receives each term, from which it selects between 150 and 200 for opinions.

Brennan, in the text of a speech prepared for delivery yesterday to the Third U.S. Circuit Judicial Conference in Philadelphia, agreed that the court is overworked and accepts too many cases for full review.

The screening process is too important to be left to others, Brennan said.

Screening keeps the justices informed about the shape of the law in the lower courts, mirrors the "nuances and trends of legal change throughout the land," and serves as a "forum" for expression and development of "interests and sensitivities of individual justices," Stevens declared.

The public dissents periodically written when the court declines to review a case have often presaged important changes in American law, Stevens declared, citing the role of such dissents in development of defendants' rights and principles of reapportionment, such as "one man, one vote."

"The choice of issues for decision largely determines the image that the American people have of their Supreme Court.... The screening function is an indispensable and inseparable part of the entire process and it cannot be withdrawn from the court without grave risk of impairing the very core of the court's unique and extraordinary functions," Brennan said.

Instead, Brennan, the most senior justice after 25 years on the court, endorsed consideration of proposals to reduce the number of cases that federal law requires the courts to review, and to create specialized courts of appeals to resolve lower-court conflicts in certain types of cases.