The Supreme Court ruled yesterday that states can refuse to spend public monies on abortions for poor mothers if the operations are deemed not medically necessary.

The justices held 6 to 3 that neither the constitutional guarantee of equal protection of the laws nor the Social Security Act requires payment for elective abortions by states that spend Medicaid funds for childbirth.

They said the federal government and the states remain entirely free to fund nontherapeutic abortions "through the normal processes of democracy."

"The issues present policy decisions of the widest concern," Justice Lewis F. Powell Jr. noted for the court. "They should be resolved by the representatives of the people, not by this court."

This declaration seems to signal the court's intent, in a pending case, to uphold a one-year ban in the Medicaid appropriations law on use of federal funds "to perform abortions except where the life of the mother would be endangered if the fetus were carried to term."

A federal judge in New York City stayed enforcement of the ban on the day it was adopted. Last week, acting on a new appropriations bill for the Department of Health, Education, and Welfare, the House strengthened the ban by forbidding the use of federal funds to pay even for abortions in women whose lives are threatened. Yesterday, the Senate Appropriations Committee voted to strike the abortion amendment from the bill with the understanding the issue would be debated by the full Senate.

The anti-abortion Americans United For Life reacted to "a significant victory for the right-to-life movement" by announcing that its legal defense fund will ask the court today to lift the judge's stay.

The American Civil Liberties Union, terming the justices' action "among the worst by a Supreme Court generally insensitive to individual rights," and Planned Parenthood Federation of America pleaded with the Senate to reject the House ban so that abortions for the poor do not become "only a theoretical right without practical meaning."

Powell said the decisions -- in cases from Pennsylvania, Connecticut, and Missouri -- signal "no retreat" from the milestone 1973 decisions in which 2, a Texas law making it a crime to the court ruled unconstitutional, 7 to procure or attempt to procure an abortion, except when a physician declared an abortion necessary to save the mother's life.

"We held that only a compelling state interest would justify such a sweeping restriction on a constitutionally protected interest, and we found no such state interest during the first trimester," Powell said.

Dissenting Justice William J. Brennan Jr. wrote, "None can take seriously the court's assurance that its conclusion signals no retreat. . . . Indeed, it cannot be gainsaid that today's decision seriously erodes the principles" laid down in the 1973 decisions "to guide the determination of what constitutes an unconstitutional infringement of the fundamental right to be free to decide whether to have an abortion."

In another dissent, Justice Harry A. Blackmun accused the majority of letting the states "accomplish indirectly" what the court in 1973, "by a substantial majority and with some emphasis . . . said they could not do directly."

Blackmun, who wrote the 1973 opinions for the court, saw a parallel between the attitude of yesterday's majority and the attitude imputed to Marie Antoinette at the time of the French Revolution.

He said that the majority concedes the existence of an indigent, financially helpless woman's constitutional right to decide the outcome of her pregnancy, "but denies the realization and enjoyment of that right on the ground that existence and realization are separate and distinct."

For her, he said, "the result is punitive and tragic. Implicit in the court's holdings is the condescension that she may go elsewhere for her abortion. I find that disingenuous and alarming, almost reminiscent of 'let them eat cake.'" He went on to say:

"There is another world 'out there', the existence of which the court, I suspect, either chooses to ignore or fears to recognize. And so the cancer of poverty will continue to grow."

Blackmun said the court "well knows" that Congress and the states are not about to authorize the use of funds for nontherapeutic abortions.

"Why," he asked, "should any politician incur the demonstrated wrath and noise of the abortion opponents when mere silence and nonactivity accomplish the results the opponents want?"

Justice Thurgood Marshall, the third dissenter, wrote that the court also "well knows" its decisions "will have the practical effect of preventing nearly all poor women from obtaining safe and legal abortions," and will "brutally coerce" them "to bear children whom society will scorn for every day of their lives."

Marshall said that opponent of abortion, failing in efforts to overturn the 1973 decisions, "have attempted every imaginable means to circumvent the commands of the Constitution and impose their moral choices upon the rest of society . . . I am appalled at the ethical bankruptcy of those who preach a 'right to life' that means, under present social policies, a bare existence in utter misery for so many poor women and their children."

Fifteen states have passed laws that deny Medicaid funds for elective abortions. In 1975, Medicaid paid for between 250,000 and 300,000 abortions, the vast majority of them elective, out of a national total of 1.1 million. In the same year, an estimated 33,000 women seeking abortions had to leave their home states to get one. Also in 1975 only 18 per cent of the nation's public hospitals performed even a single abortion, and in 10 states not one provided abortion services.

At present there are no similar restrictions on the use of Medicaid funds for elective abortions in Maryland, Virginia or the District of Columbia.

Marshall said that nonwhite women will be principally affected by the decisions, because, he calculated, the proportion among them relying on Medicaid is about 38.5 per cent, compared with about 7 per cent among white women.

Each of the three decisions reversed or nullified a ruling by a U.S. Court of Appeals.

In the Pennsylvania case (Beal vs Doe), the core issue was a state plan limiting Medicaid for abortions in the first six months of pregnancy to those certified to be "medically necessary."

For the court, Powell wrote that "the only question" was whether the Social Security Act, which grants the states broad discretion, required Pennsylvania to fund all abortions that are legally permissible. Nothing in the legislative history suggests that it was unreasonable for a state to act as did Pennsylvania to implement its "unquestionably strong and legitimate interest in encouraging normal childbirth," he wrote.

Dissenting, Brennan said that Congress had intended to recognize pregnancy as a condition requiring medical services and to prevent government interference with the decision of the woman and her doctor about which services to provide.

In the Connecticut case (Maher vs. Roe), the key issue was whether a state that pays Medicaid payments for childbirth denies equal protection of the laws by paying only for medically necessary first-trimester abortions.

Powell wrote that Connecticut "places no obstacles -- absolute or otherwise -- in the pregnant woman's path to an abortion. An indigent woman who desires an abortion suffers no disadvantage as a consequence of Connecticut's decision to fund childbirth: she continues as before to be dependent on private sources for the service she desires."

Denying a "retreat" from the 1973 decisions, Powell emphasized "a basic difference between direct state interference with a protected activity and state encouragement of an alternative activity consonant with legislative policy."

He rejected Brennan's charge that the Connecticut regulation "is an obvious impairment of the fundamental right," established in 1973, of a pregnant woman to have an abortion, and that in upholding it the court "makes new law."

The Missouri case (Poelker vs. Doe) came from St. Louis, where Mayor John H. Poelker had campaigned for office with a pledge to refuse to permit elective abortions to be performed at a city-owned hospital.

In an unsigned opinion, the court held "that the Constitution does not forbid a state or city, pursuant to democratic processes, from expressing a preference for normal childbirth as St. Louis has done.

Marshall described the restrictions in all three cases as "the most vicious attacks yet devised" on the right of poor women to have abortions.