WASHINGTON -- When the Senate Judiciary Committee votes on the Supreme Court nomination of Samuel A. Alito Jr. today, all 10 Republicans on the panel are expected to vote yes and all eight Democrats no -- including three who voted to confirm Chief Justice John G. Roberts Jr.

A slightly less lopsided partisan split seems likely on the Senate floor.

Explanations abound for why Democratic senators are lining up against Judge Alito: Unlike the chief justice, who replaced the late William H. Rehnquist, a conservative, Judge Alito has been named to replace a swing vote, Justice Sandra Day O'Connor. Another factor is lingering Democratic anger that Mr. Bush yanked the Supreme Court nomination of White House Counsel Harriet Miers after an outcry from social conservatives, who have embraced Judge Alito.

But there is another element in the emerging partisan split : Judge Alito's testimony before the Senate Judiciary Committee on abortion and executive power

Like Chief Justice Roberts, Judge Alito acknowledged that Roe v. Wade, the 1973 decision legalizing abortion, was an important precedent entitled to respect. But despite prompting in a letter from committee chairman Sen. Arlen Specter, R-Pa., an abortion-rights supporter, Judge Alito did not follow Chief Justice Roberts' example by saying that overturning a precedent like Roe causes a "jolt to the legal system."

And while Judge Alito indicated he would begin any analysis of a future abortion case with the 1992 precedent of Planned Parenthood v. Casey, which reaffirmed the essential holding of Roe, he said he might not stop there.

The nominee also raised eyebrows when he said that following precedent, while important, is not an "inexorable command" for Supreme Court justices.

Finally, Judge Alito refused to say that Roe v. Wade was as sacrosanct as other landmark rulings, such as the 1954 Brown v. Board of Education rulings outlawing segregated public schools.

Finally, there was Judge Alito's answer to a question about Kelo v. New London, the controversial decision earlier this year in which the court ruled 5-4 (with Justice O'Connor dissenting) that a city in Connecticut could use eminent domain to acquire homes and businesses for a redevelopment plan that benefited a private business.

Judge Alito acknowledged that "when someone's home is being taken away, using the power of eminent domain, that is a blow to a lot of people," but he added that, like Roe v. Wade, the precedent of the Kelo decision would have to be considered, but that other factors then could be weighed too.

On executive power, Judge Alito repeatedly told the committee that the president was not above the law. He also endorsed a now-famous declaration by Justice O'Connor that "a state of war is not a blank check for the president when it comes to the rights of the nation's citizens."

Judge Alito also said he would be guided in cases dealing with presidential power by the approach outlined by Justice Robert H. Jackson in a 1952 decision overturning President Harry S. Truman's seizure of the steels mills. In his opinion in that case, Justice Jackson wrote that "when the president takes measures incompatible with the expressed or implied will of Congress, his power is at its lowest ebb."

But Judge Alito wouldn't say whether he thought Mr. Bush's decision to authorize warrantless wiretapping of Americans by the National Security Administration violated the 1978 Foreign Intelligence Surveillance Act in which Congress required the president to seek surveillance warrants from a secret court.

As he had done with other issues that he said were "in play," Judge Alito observed that the legality of the president's action "is very likely to result in litigation in the federal courts." But he didn't seem to view the issue as open-and-shut.

He suggested that, if the issue reached the Supreme Court, the justices might determine that the requirements of the FISA law were modified by the resolution Congress passed after Sept. 11, 2001 authorizing the president to "use all necessary and appropriate force" against terrorists.