The Supreme Court yesterday stood firmly behind its 1973 decision legalizing abortion and ruled 6 to 3 that government cannot interfere with this "fundamental right" of women unless it is clearly justified by "accepted medical practice."

The court struck down laws, similar to those in 22 states, that require hospitals, rather than clinics, to perform abortions after the first three months of pregnancy. This should make relatively inexpensive abortions in clinics even more widely available than they are now, especially in parts of the country where hospitals, often under political pressure, have stopped performing abortions.

The court majority also invalidated an Akron, Ohio, ordinance requiring a 24-hour waiting period and elaborate "informed-consent" procedures before an abortion can be performed, and special "decent burial" rules for disposal of the fetus afterward. The Akron ordinance was designed by opponents of abortion as a national model for such restrictions.

The combined effect of yesterday's rulings will make it much more difficult for cities, states or even the federal government to legally defend incremental encroachments on access to abortions.

The Supreme Court acted after a decade of intense national debate, legal skirmishing and legislative struggle generated by its 1973 decision. At times, the abortion issue has dominated political campaigns, disrupted Congress and state legislatures, and sparked controversy over judicial appointments, including President Reagan's elevation of Sandra Day O'Connor to the Supreme Court.

She showed her colors yesterday by leading the dissent against the court's majority. The only woman justice, joined by Justices Byron R. White and William H. Rehnquist, challenged the validity of much of the 1973 abortion decision and agreed with the Reagan administration's contention that the court was intruding on legislative authority.

Outraged opponents of abortion yesterday vowed to fight back against the decision and push even harder for a constitutional amendment that would ban abortion nationwide or allow the states to prohibit it.

All the restrictions on abortion struck down by the court yesterday had been enacted at the urging of anti-abortion forces. The court said none of them was sufficiently related to the safety and health of women. All of them, Justice Lewis F. Powell Jr. wrote for the court majority, made abortions more expensive or more risky to health and all improperly substituted the judgment of legislators for the judgment of physicians and women.

The majority rejected the Reagan administration's contention that the court should back away from its own precedent. "We respect it today, and reaffirm Roe v. Wade," Powell said, reading these words from the bench for added emphasis.

The ruling actually expanded the 1973 decision, which had appeared to allow hospitalization requirements after the first trimester (the first 12 weeks) of pregnancy. Powell said improved medical technology, allowing safe abortions outside of hospitals, justified allowing abortions in clinics.

"We did not persuade a majority," Solicitor General Rex E. Lee, who represented the Reagan administration in the case, said yesterday. But "we got three solid votes. We may yet live to fight another day."

O'Connor wrote that the court can and should correct "errors" of constitutional judgment in past decisions. This was a victory for Reagan. He had nominated her in the face of angry criticism from anti-abortion conservatives who doubted her loyalty to their cause.

But her dissent yesterday drew bitter denunciations from some women's rights advocates, who earlier had been pleasantly surprised by her votes on other women's issues. It "was unprincipled," charged Janet Benshoof, the American Civil Liberties Union lawyer who argued in favor of yesterday's ruling.

"I'm personally disappointed," said Jane Gruenebaum, spokesman for the National Abortion Federation. "It would have been nice to have a woman on the Supreme Court who was a stronger advocate of a woman's right to abortion."

The court did give abortion foes minor victories by upholding, as it has in the past, laws requiring parental consent to an abortion for a woman under 18, as long as she can freely appeal to a local court if she is unable to obtain such permission.

It also upheld Virginia's law requiring that abortions in the second trimester of pregnancy be performed in hospitals and upheld the conviction of a Northern Virginia physician, Dr. Chris Simopoulos, for performing an abortion in his office. The Virginia law is valid, the justices ruled, only because the state includes licensed outpatient clinics in its definition of hospitals and does not ban abortions in them.

Roe v. Wade, which struck down abortion bans across the country, remains one of the most controversial decisions ever made by the Supreme Court. It said no interference with abortion is permissible during the first three months of pregnancy (the first trimester), but that in the second three months, regulations can be imposed to protect the health of the mother. Abortions in the final stage in some circumstances may be "proscribed," the court said in 1973.

Yesterday's ruling in the Akron case guided the outcome of the Virginia case and another from Missouri.

Powell said the second trimester hospitalization requirement in the Akron ordinance "places a significant obstacle in the path of women seeking an abortion." Powell said an abortion may cost twice as much in a hospital as in a clinic. Because Akron hospitals rarely perform such abortions, he added, the requirement "may force women to travel to find available facilities, resulting in both financial expense and additional health risk."

He acknowledged that the 1973 Roe v. Wade ruling gave legislators more leeway to regulate second-trimester abortions because of the increased risk to the women. Since then, however, Powell said the development of safer abortion techniques--particularly the dilation and evacuation (D&E) procedure--has reduced that risk. He cited studies by the American Public Health Association and the American College of Obstetricians and Gynecologists.

"By preventing the performance of D&E abortions in an appropriate non-hospital setting, Akron has imposed a heavy, and unncessary, burden on women's access to a relatively inexpensive, otherwise accessible, and safe abortion procedure," Powell wrote.

Akron's 24-hour waiting period also is unnecessary, unless prescribed by a doctor, Powell said, concluding that "there is no evidence" suggesting that the abortion will be safer because of the wait. "If a woman, after appropriate counseling, is prepared to give her written informed consent and proceed with the abortion, a state may not demand that she delay the effectuation of that decision," he said.

The "informed consent" provision of the Akron ordinance required physicians to tell a woman about the "development of her fetus," the physical and emotional complications that may result from an abortion, and the availability of agencies to assist her with birth control, adoption and childbirth.

That provision, Powell said, appeared designed not to inform her of her choice but to "persuade her to withhold it altogether." Governments, he said, do not have "unreviewable authority to decide what information a woman must be given before she chooses to have an abortion . . . . It remains primarily the responsibility of the physician . . . ."

O'Connor's dissent stopped short of saying she would overrule Roe v. Wade, though Powell, in a footnote, suggested she would, in effect, do that.

Saying the court has been too strictly scrutinizing abortion regulations, she attacked the trimester scheme of Roe v. Wade as "unworkable."

She said government should be free to impose some regulation at all stages of pregnancy, both to protect maternal health and the "potential life" of the fetus. "The state's interest in protecting potential human life exists throughout the pregnancy," she said.

Citing language in previous opinions, she said "we must always be mindful that 'the Constitution does not compel a state to fine-tune its statutes so as to encourage or facilitate abortions. To the contrary, state action encouraging childbirth except in the most urgent circumstances is rationally related to the legitimate government objective of protecting potential life.' "

The dissent particularly criticized Powell's conclusion that second trimester abortions are now safer. She said new medical advances also have made it easier for fetuses to survive earlier outside the womb. The majority opinions in the Akron case and in the 1973 ruling forces courts, she said, to "pretend to act as science review boards and examine . . . legislative judgments."

The Missouri decision (Planned Parenthood Association of Kansas City v. Ashcroft) also struck down a hospitalization requirement. But it upheld laws requiring special pathology reports on the aborted fetus and the participation of a second physician in the few abortions performed in the last period of pregnancy to be on hand in the event of a live birth.