WASHINGTON -- Justice Sandra Day O'Connor has been a steadfast supporter of abortion rights on the Supreme Court. Judge Samuel A. Alito Jr., the man nominated by President Bush to succeed her, is hostile to Roe v. Wade and almost surely would vote to overturn that precedent.

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That is the conventional wisdom as the Senate Judiciary Committee prepares to question Judge Alito, but it is a simplistic picture that smooths over changes and complexities in both judges' writings about abortion.

It is possible that, once on the court, Judge Alito would be more willing than Justice O'Connor to uphold restrictions on abortion, particularly those designed to protect the interests of husbands of women contemplating the procedure.

But the evidence offered for that proposition -- Judge Alito's dissenting opinion in a 1991 Pennsylvania case -- isn't the smoking gun his critics say it is.

In Casey v. Planned Parenthood of Southeastern Pennsylvania, a three-judge panel of the 3rd U.S. Circuit Court of Appeals upheld the constitutionality of several amendments to the 1982 Pennsylvania Abortion Control Act, including a 24-hour waiting period and a requirement that women give "informed consent" to the procedure. But the majority struck down a provision requiring married women considering an abortion to notify their husbands.

Judge Alito dissented from that last holding. After concluding that the spousal-notification requirement didn't constitute an "undue burden" on a woman's right to abortion, Judge Alito then asked whether it served a reasonable purpose. He answered yes, pointing to a married man's "interest in the welfare of a fetus he has conceived with his wife."

Alito continued: "The Pennsylvania legislature could have rationally believed that some married women are initially inclined to obtain an abortion without their husbands' knowledge because of perceived problems -- such as economic constraints, future plans, or the husbands' previously expressed opposition -- that may be obviated by discussion prior to the abortion."

When the U.S. Supreme Court reviewed the decision in a 1992 case that became a landmark, it affirmed the 3rd Circuit in upholding most provisions of the law, while reaffirming the "essential holding" of Roe v. Wade that the Constitution protected a right to abortion.

But, like the majority of the 3rd Circuit, the high court ruled that the spousal notice provision was unconstitutional. In the main opinion, written by Justice O'Connor and Justices Anthony Kennedy and David H. Souter, the court said the spousal notification provision "does not merely make abortions a little more difficult or expensive to obtain; for many women, it will impose a substantial obstacle."

Justice O'Connor and her colleagues went on to say that even though the spousal-notification provision allowed for exceptions for abusive violent family situations, "we must not blind ourselves to the fact that the significant number of women who fear for their safety and the safety of their children are likely to be deterred from procuring an abortion [by this provision] as surely as if the Commonwealth had outlawed abortion in all cases."

Although most of the attention since Judge Alito's nomination has focused on the contrast between his and Justice O'Connor's positions on spousal-notification, there may be much less to the difference than meets the eyes.

In 2005, 13 years after the Supreme Court reaffirmed a constitutional right to abortion in the Casey decision, it is often forgotten that Roe v. Wade and abortion rights appeared to be in trouble in the 1980s -- partly because of criticism of the 1973 decision by recently appointed justices including Sandra Day O'Connor.

In a series of cases, Justice O'Connor questioned the logic and practicality of the so-called trimester framework of Roe: that abortion could not be regulated at all by the state during the first three months of pregnancy; that it could be regulated to protect the mother's health during the second three months; and that it could be regulated or even outlawed (except when the mother's health was threatened) to protect the viable fetus during the final three months.

In a 1983 dissent from the majority's holding that it was unconstitutional for the city of Akron, Ohio, to require that abortions after the first trimester be performed in hospitals, Justice O'Connor proposed a different legal standard for deciding whether a restriction on abortion violated the Constitution -- one that worried abortion-rights supporters at the time.

First, Justice O'Connor wrote, the court should determine whether a particular restriction was an "undue burden" on the right to abortion. Only if the answer was yes would the court go on to subject the regulation or law to "strict scrutiny," which means that a regulation is upheld only if it serves a "compelling government interest" and does so by the "least restrictive means."

This was essentially the test that Judge Alito and his colleagues used in 1991 when they considered the constitutionality of the Pennsylvania Abortion Control Act. The majority found that the spousal notification requirement was an undue burden; Judge Alito came to the opposite conclusion.

At Step One of Justice O'Connor's two-step process, he determined that there was no undue burden because the spousal notification provision did not give the husband veto power. Judge Alito quoted Justice O'Connor as saying that an undue burden would not be created by "a state regulation [that] may 'inhibit' abortions to some degree."

Then having determined that the requirement wasn't an undue burden, Judge Alito moved to Step Two -- identifying a "compelling interest" -- and found it in a married man's "interest in the welfare of a fetus he has conceived with his wife."

But surely Judge Alito must have misread Justice O'Connor's test, if Justice O'Connor came to the opposite conclusion when the Pennsylvania law reached the Supreme Court? Not necessarily.

Kathryn Kolbert, the lawyer who argued the Casey case for Planned Parenthood, said it was Justice O'Connor who changed between the 1980s, when she floated the "undue burden" test, and the court's 1992 decision in Casey in which she used that formula to preserve most of the protections of Roe v. Wade.

"O'Connor's view of what was an 'undue burden' changed significantly," Ms. Kolbert said yesterday. "The Casey opinion was one of the most feminist decisions in history."

This does not guarantee that Judge Alito, if confirmed by the Senate, would follow Justice O'Connor in redefining "undue burden" in a way that expanded abortion rights.

Nor does it shed light on whether he believes Roe v. Wade or Planned Parenthood v. Casey is, in Sen. Arlen Specter's term, a "super-precedent" worth special respect.

But the evolution of the "undue burden" test does suggest that the contrast between Justice O'Connor and Judge Alito may, like much of what is said during a Supreme Court confirmation, may be overstated.