As the Senate confirmed Justice Alito to the Supreme Court yesterday, two federal appeals courts issued rulings that called attention to the pivotal role the new justice could play in the epic battle over abortion rights.

The 2nd Circuit Court of Appeals, based in New York, and the 9th Circuit, headquartered in San Francisco, both upheld lower court decisions that found unconstitutional a law Congress passed in 2003, the Partial-Birth Abortion Ban Act. Last year, another appeals court, the St. Louis-based 8th Circuit, blocked enforcement of the same law.

Attorneys involved in the abortion cases said the opinions issued almost simultaneously yesterday on each coast should coax the court into taking another look at the question. Justice Alito could have a decisive impact, reversing the court’s stance on the partial birth abortion ban, according to advocates on both sides of the debate.

“All this points to the Supreme Court granting review sooner rather than later,” a lawyer who regularly argues for conservative causes at the high court, Jay Sekulow, told The New York Sun.

In a 2000 case, Stenberg v. Carhart, the Supreme Court ruled, 5-4, that a Nebraska law aimed at prohibiting partial-birth abortions was unconstitutional because it lacked an exception for women who needed the procedure to preserve their health.

Mr. Sekulow said the departure of Justice O’Connor, who joined with the majority in that case, and her replacement with Justice Alito, makes it likely the court will reach a different result if it revisits the issue. “It was 5-4 against us. Now I think it will be 5-4 for us. The Alito confirmation, I think, changes the way this one comes out,” Mr. Sekulow, who heads the American Center for Law and Justice, a conservative legal group, said.

Abortion rights proponents also said the changes to the makeup of the court could make it less willing to block restrictions on abortion, such as bans on partial birth abortions, including a procedure doctors call dilation and extraction.

“With Justice O’Connor gone and Justice Alito on the bench, it’s a very different picture and one that is ominous for women’s health,” an attorney for Planned Parenthood, Eve Gartner, told the Sun. “From everything we know about Justice Alito, he’s not going to protect a woman’s right to choose or a woman’s right to health and safety. The loss of Justice O’Connor is a crucial loss,” said Ms. Gartner, who added that the litigation over the 2003 federal abortion law is “clearly heading to the Supreme Court.”

President Bush’s nomination of Samuel Alito Jr. to the court was formally confirmed by the Senate in a 58-42 vote yesterday morning. The roll call produced few surprises. All Senate Republicans except for Senator Chafee, of Rhode Island, voted in favor of Justice Alito, as did four Democrats, Senators Byrd, of West Virginia; Conrad, of North Dakota; Johnson, of South Dakota, and Nelson, of Nebraska. The remainder of the Democrats voted to reject the selection.

Justice Alito was sworn in a short time later by Chief Justice Roberts in a ceremony that took place in the conference room where Supreme Court justices discuss cases, according to a court spokeswoman, Kathy Arberg. A more formal investiture ceremony will be scheduled later, she said.

In its 2-1 decision yesterday, the 2nd Circuit panel relied on the Supreme Court’s finding from the Stenberg case that abortion restrictions were unconstitutional if “substantial medical authority” indicated that the restriction could hurt the health of women.

“Unquestionably such ‘substantial medical authority’ exists,” Judge Jon Newman wrote, in an opinion joined by Judge John Walker Jr., reviewing the challenge brought in New York. “It is abundantly revealed in the evidence presented both to the trial court in this litigation and to the Congress in the hearings that preceded the act,” Judge Newman, who was appointed by President Carter, said.

In dissent, an appointee of President Clinton, Judge Chester Straub, stressed that the district court in Manhattan that considered the legal challenge found that the doctors who testified in favor of the procedure produced no credible evidence that it is safer than more common abortion methods. The lower court found, however, that the fact that reputable doctors believed the procedure was safer for some patients meant it could not be banned.

Judge Straub said the courts have a duty to make their own assessment of the need for the procedure, especially in light of Congress’s finding that the dilation and extraction technique “is never necessary.”

“We should consider independently whether providing an unknown number of women a marginal health benefit outweighs both the fetus’s emerging right to life and the state’s interests in protecting actual and potential life,” Judge Straub wrote. “Allowing a physician to destroy a child as long as one toe remains within the mother would place society on the path towards condoning infanticide.”

Judge Walker penned a concurring opinion in which he adopted Judge Newman’s analysis of the law but expressed sympathy for Judge Straub’s distress with the outcome of the case.

“In today’s case, we are compelled by a precedent to invalidate a statute that bans a morally repugnant practice, not because it poses a significant health risk but because its application might deny some unproven number of women a marginal health benefit,” wrote Judge Walker, who was appointed by and is a cousin of President George H.W. Bush. Judge Walker called the Stenberg precedent “flawed” and said it presented legislators seeking to regulate abortion with “a virtually insurmountable evidentiary hurdle.”

The 2nd Circuit judges called for further arguments from the parties on whether the whole congressional statute should be blocked or whether it could be salvaged in part by the court.

While the 2nd Circuit’s ruling was something of a grudging victory for abortion rights advocates, the 9th Circuit’s decision was a sweeping and unequivocal win. The 9th Circuit panel ruled, 3-0, that the anti-partial-birth law was unconstitutional on three separate grounds. The judges faulted the statute not only for the lack of an exception protecting the health of the mother, but also for vagueness and for prohibiting some first-trimester abortions.

All three judges on the case were Democratic appointees.