The reactions of interest groups on the political right and left signaled that the much-anticipated battle among such organizations over O'Connor's successor might finally begin.

Within minutes of the announcement, liberal groups such as People for the American Way, Planned Parenthood and the Alliance for Justice announced battle plans.

"You name it, we'll do it" to oppose Alito, said Nan Aron, president of the Alliance for Justice. E-mail and letter-writing campaigns are in the works, as well as television ad campaigns, with the focus on states with moderate senators from both parties who in the past have been supportive on issues such as abortion rights.

At the same time, conservative groups such as Progress for America, the Committee for Justice and the American Center for Law & Justice were quick to offer their enthusiastic support. They, too, have dissected Alito's judicial opinions and legal writings and think he would be just the kind of Supreme Court justice they've wanted.

"President Bush promised that he would nominate justices in the mold of Justices (Antonin) Scalia and (Clarence) Thomas. In choosing Judge Alito for the high court, President Bush has done just that," said Jay Sekulow, chief counsel to the American Center.

After largely sitting out the confirmation of John Roberts for chief justice, and leaving the Miers battle to intramural squabbling on the right, both sides appear ready to engage.

"Interest groups are going to come out strong on this nomination" because Alito has a long, clear record as a conservative judge, says Michael Gerhardt, professor of constitutional law at the University of North Carolina School of Law. "I don't think that's necessarily good. The word I would use is regrettable. It will be all about catch phrases and code words, not an elevated debate about the law."

"We're going to have a huge fight, which is going to come down to a fight over abortion," said Jim Duffy, a Democratic political strategist.

"People who are worried about paying high gas prices are going to be asking, 'Where are my interests in this?' It's a huge Washington issue, but much ado about nothing for the rest of the country."

Alito so resembles Scalia in his judicial outlook that he has been tagged with the nickname "Scalito." But while the two share conservative credentials, Alito lacks Scalia's fiery, provocative style. In 15 years on the 3rd Circuit, he has been a reliable vote for a narrow interpretation of constitutional rights.

The Alito opinion likely to generate the most debate in the coming weeks came in a 1991 abortion rights case. Alito was the sole vote to uphold a Pennsylvania law requiring women to notify their husbands before obtaining an abortion. Alito's dissenting view was later rejected by the U.S. Supreme Court.