A household mailbox is an exclusive sanctuary for stamped mail and cannot be used as a convenient deposit point for unstamped pamphlets and flyers from local civil associations, the U.S. Supreme Court ruled yesterday.

A coalition of suburban New York civic groups had argued that a federal law which makes it a crime to put unstamped circulars in a mailbox violated their constitutional rights under the First Amendment to freedom of speech and press.

In a 7-to-2 decision, the majority of the court agreed that a ressidential mailbox should not be stuffed with unpaid notices from local community groups and upheld the federal law, but they differed on the reasons.

Justice William H. Rehnquist, joined by four colleagues, concluded that just because an officialmailbox is pary of the government's nationwide postal system that does not mean it is a public forum, like a street corner or a park, where the First Amendment would give limited guarantees of access to anyone with a message.

If civic groups were permitted to intrude into mailboxes and stuff them with unpaid notices it would interfere with the safe and efficient operation of the postal system, Rehnquist said.

In reversing a lower court decision, Rehnquist noted the federal law challenged by the civic groups prohibited deposit of all unstamped circulars or notices in official mailboxes and did not consider the content of the communications. Moreover, Rehnquist said, the civic groups can get messages to their members in other ways.

He was joined by Chief Justice Warren E. Burger and Justices Potter Stewart, Harry A. Blackmun and Lewis F. Powell Jr.

In separate concurring opinions, Justices William J. Brennan Jr. and Byron R. White disputed Rehnquist's finding that the postal system is not a public forum, although they agreed civic groups should not intrude on the mailbox.

Brennan said the federal law that blocks unstamped mail in letter boxes is a reasonable restriction because it is applied equally to all mail, because it prevents loss of postage revenues and because there are alternate means of communication available to the civic groups.

White wrote that the postal system is a public forum for anybody who will pay the postage fee to use it. The government has an interest in defraying costs of the postal system, White wrote, and "it is clear that stuffing the mailbox with unstamped materials is a burden on the system."

In a separate dissenting opinions, Justices Thurgood Marshall and John Paul Stevens agreed that if overstuffed mailboxes are a threat to the efficiency of the mails, there are less drastic means to cut the flow of such notices, such as the equivalent of a "no trespassing" sign on a mailbox.

As it stands now, the dissenting justices said, the blanket prohibition on unstamped mail impedes the free flow of communcation.

In other actions yesterday, the court unanimously ruled individuals do not have the right to sue for money damages in water pollution cases. The justices reversed a lower court decision which would have allowed the National Sea Clammers Association to move ahead with a multimillion-dollar claim that fishing grounds off the New York and New Jersey coasts were seriously damaged by the dumping of sewage and other wastes.

Powell, writing for the court, said the federal Walter Pollution Control Act and the 1972 Marine Protection, Research and Sanctuaries Act set out elaborate remedies to protest such pollution, but did not intend that citizens be allowed to sue for money damages. Rather, both provide only that citizens can seek court orders to block pollution and to require federal officials to enforce the laws.

In a 6-to-3 decision, the high court also reversed a lower court decision and upheld federal regulations which allow states to consider a spouse's income when the calculate the amount of Medicaid benefits owed to an applicant.

The Gray Panthers, an interest group represinting elderly persons, had taken the regulations to court on behalf of applicants living in institutions, arguing the government should determine need in such cases on an individual basis and not by general formulas. The three dissenters were Stevens, Marshall and Brennan.