The Supreme Court yesterday struck down a Minnesota law that required pregnant teenagers to inform both parents before obtaining an abortion, but said that such laws are constitutional if they give minors the opportunity to ask a judge to waive the notification requirement.

The court divided 5 to 4 on both aspects of the decision, with Justice Sandra Day O'Connor the pivotal vote.

In her first vote to strike down an abortion restriction, O'Connor agreed with the court's liberals that a simple requirement that a pregnant minor inform both her parents before getting an abortion is unconstitutional.

But she voted with conservatives to find that the two-parent notification requirement is constitutional as long as a minor has the opportunity to convince a judge that informing one or both parents would not be in her best interest, or that she is mature enough to make the abortion decision on her own.

The justices faced this dual decision because Minnesota had enacted two alternative forms of the law, and both were appealed to the Supreme Court.

A year ago the court made new law by giving the states wider leeway to restrict the right to abortion. In effect, yesterday's rulings set new limits on states' freedom to limit abortion.

The decision in Hodgson v. Minnesota represented a defeat for the Bush administration, which had urged the court to use the case to reverse the 1973 Roe v. Wade decision and rule that there is no fundamental constitutional right to an abortion. At the least, Solicitor General Kenneth W. Starr argued, the court should find that minors have no fundamental right to an abortion without their parents' knowledge.

But abortion rights activists said yesterday they considered the new decisions a defeat for them. They complained that the court had in effect invited states to pass legislation requiring pregnant teenagers to notify their parents about planned abortions. Several abortion-rights activists expressed alarm that a majority of the justices no longer appear to be treating abortion as a fundamental constitutional right, and has relaxed its standard for testing other kinds of abortion restrictions.

Antiabortion groups generally praised the decision and said it would spur them to continue efforts to enact further restrictions in state legislatures across the country.

Justice John Paul Stevens, in the opinion striking down the two-parent notice requirement without the option of going to court, said that in "the ideal family setting" both parents would know about their daughter's pregnancy.

But he said the two-parent notification mandated in Minnesota -- where only half the state's minors live with both biological parents -- "proved positively harmful to the minor and her family," forcing the involvement of parents who had deserted or abused their children.

Justices William J. Brennan Jr., Thurgood Marshall and Harry A. Blackmun joined in the ruling.

O'Connor agreed that the law was "unreasonable" without the so-called judicial bypass provision allowing a minor to go to court to try to avoid notifying her parents. But O'Connor said the law "passes constitutional muster because the interference with the internal operation of the family . . . simply does not exist where the minor can avoid notifying one or both parents by use of the bypass procedure."

Chief Justice William H. Rehnquist and Justices Byron R. White, Antonin Scalia and Anthony M. Kennedy voted to uphold the law, saying it was constitutional with or without the judicial bypass.

In a second abortion case, the court voted 6 to 3 to uphold a 1985 Ohio law requiring a physician to notify one parent of a pregnant minor of her intent to have an abortion. The law also contained a judicial bypass provision but required the minor to prove by "clear and convincing" evidence that she should not be required to notify a parent.

Kennedy, writing for the majority in the Ohio case, Ohio v. Akron Center for Reproductive Health, said the law, including the heightened standard of proof, "does not impose an undue, or otherwise unconstitutional, burden on a minor seeking an abortion."

In earlier decisions on parental consent laws, the court has said states cannot give parents an absolute "veto" over their daughters' abortion decisions and that consent laws must contain a judicial bypass provision. Yesterday's decisions left open the question of whether a law requiring notification of only one parent might be constitutional even without a judicial bypass provision.

The Minnesota law, enacted in 1981, requires a pregnant minor to notify both parents of her intent to have an abortion -- even if, for example, she does not live with her father or has never met him, or if he has a history of violence or abuse. The law imposes a 48-hour waiting period after notification, a provision also upheld yesterday. Knowing the law would be constitutionally challenged, the state legislature simultaneously passed another version containing the judicial bypass provision.

The law was in effect 1981-86 with the judicial bypass provision. Judges refused to allow abortion in just nine of more than 3,500 cases.

The state argued that its interest in ensuring that parents are involved in critical decisions by their children should allow it to require notification of both parents in all circumstances. It sought to do away with the need for judicial involvement.

Abortion rights advocates argued that the law was unconstitutional even with the bypass provision because it had become clear in practice that forcing minors to go to court was a traumatic experience that interfered with their privacy rights and did not promote family unity or communication.

A federal appeals court said the law was constitutional with the bypass provision, but not without it.

In affirming both parts of that decision yesterday, the court once again displayed its deep divisions on the abortion question, issuing five separate opinions.

Kennedy, joined by Rehnquist, White and Scalia in dissenting from the majority opinion requiring that a pregnant teenager have the option of going to court, argued passionately that parents have a right to be informed of their daughters' medical decisions.

Kennedy said the law was constitutional although "it does remain possible . . . that in some instances notifying one of both parents will not be in the minor's best interests."

He said the state "has done no more than act upon the common-sense proposition that, in assisting their daughter in deciding whether to have an abortion, parents can best fulfill their roles if they have the same information about their own child's medical condition and medical choices as the child's doctor does; and that to deny parents this knowledge is to risk, or perpetuate, estrangement or alienation from the child when she is in the greatest need of parental guidance and support."

Marshall, joined by Brennan and Blackmun, contended with equal vigor that the law was unconstitutional even with bypass provisions. Stevens agreed, in a separate opinion.

"This scheme forces a young woman in an already dire situation to choose between two fundamentally unacceptable alternatives: notifying a possibly dictatorial or even abusive parents and justifying her profoundly personal decision in an intimidating judicial proceeding to a black-robed stranger," Marshall wrote. "For such a woman, this dilemma is more likely to result in trauma and pain than in an informed and voluntary decision."

But Marshall also said the ruling "reaffirms the vitality of Roe," because the court's majority implicitly reaffirmed a woman's constitutional right to have an abortion. But abortion-rights activists said they thought Marshall was being too optimistic in his reading of the opinion.

The decision in the Ohio case also produced four separate opinions, including a plea from Scalia that the court recognize that the Constitution contains no right to abortion and "end its disruptive intrusion into this field as soon as possible."

A federal appeals court struck down the Ohio law on the grounds that several of its provisions -- the clear and convincing standard, the requirement that the notice be provided directly by the physician, and the potential for delays while a judge reviews the request -- violate minors' constitutional rights. It has never been put into effect.

In upholding the law yesterday, Kennedy said that "it is both rational and fair for the state to conclude that, in most instances, the family will strive to give a lonely or even terrified minor advice that is both compassionate and mature."

Blackmun, dissenting with Brennan and Marshall, said the law forces "vulnerable and powerless young women" to "wend {their} way" through an "obstacle course" of regulations.