WASHINGTON - The Supreme Court steered clear of a major ruling on abortion Wednesday, instead giving New Hampshire a chance to save its parental notification law.

Justices, in a rare unanimous abortion ruling, agreed that the New Hampshire law could make it too hard for some ill minors to get an abortion, but at the same time they were hesitant about stepping in to fix the 2003 statute. They told a lower court to reconsider whether the entire law is unconstitutional.

"Making distinctions in a murky constitutional context, or where line-drawing is inherently complex, may call for a `far more serious invasion of the legislative domain' than we ought to undertake," retiring Justice Sandra Day O'Connor wrote for the court.

The New Hampshire case had been expected to be much closer at the high court.

Instead, justices found consensus on narrow grounds, that a lower court went too far by permanently blocking the law that requires a parent to be told before a minor daughter ends her pregnancy.

Civil rights groups predicted that the appeals court would again strike down the law.

"It tells politicians that they must include protections for women's health and safety when they pass abortion laws," said Jennifer Dalven, an attorney with the American Civil Liberties Union.

O'Connor, a key swing voter at the court on abortion rights, last year announced plans to retire and she will step down soon if the Senate confirms nominee Samuel Alito.

Alito was questioned extensively last week during his Senate confirmation hearing about his views on abortion, including the 1973 Roe v. Wade ruling that declared abortion a fundamental constitutional right. He steadfastly refused to agree with assertions by Democrats that Roe v. Wade is "settled law."

O'Connor, who supports Roe, made clear that the court was not going to break new ground in what may be her final days on the bench. "We do not revisit our abortion precedents today," she wrote in the opening of the brief opinion.

David Garrow, a Supreme Court historian at Cambridge University, said the decision "can be read as another step toward a long-term middle-ground truce, or at least stalemate."

The case returns to the 1st U.S. Circuit Court of Appeals in Boston, which had ruled that the law was unconstitutional. The statute requires that a parent be informed 48 hours before a minor child has an abortion but makes no exception for a medical emergency that threatens the youth's health.

Phyllis Woods, a former state representative from Dover, N.H., who was a main sponsor of the bill, said she was pleased by the ruling but concerned that the appeals court might require a broad health exception. "Our concern has always been that a blanket health exception opens the door and really negates the whole purpose of the bill," Woods said.

New Hampshire's appeal gave the court a chance to clarify when laws pose an "undue burden" on a woman in choosing to end a pregnancy. O'Connor is an architect of the undue burden standard, and was the deciding vote in the last abortion case in 2000, when the justices ruled that a Nebraska law banning a type of late-term abortion was too burdensome. That law did not have an exception to protect the mother's health.

Justices did not deal directly with that question, although O'Connor wrote: "under our cases it would be unconstitutional to apply the act in a manner that subjects minors to significant health risks."

"In the case that is before us ... the lower courts need not have invalidated the law wholesale," O'Connor wrote. "Only a few applications of New Hampshire's parental notification statute would present a constitutional problem."

The opinion, just 10 pages, was a partial victory for New Hampshire in a case that had been closely watched by other states with restrictions. Justices had been told that 24 states mandate a parent's approval and 19, including New Hampshire, demand parental notice.

Another major case awaiting justices is the Bush administration's appeal of a lower court ruling that struck down a federal ban on a late-term procedure that critics call "partial birth" abortions. The federal law has no health exception.

The case is Ayotte v.Planned Parenthood, 04-1144.