Democrats said on Wednesday that Samuel Alito's confirmation was not guaranteed as senators kept the focus on a 20-year-old document in which the Supreme Court nominee asserted that the Constitution "does not protect a right to an abortion."

"Anyone who thinks that this nomination is a foregone conclusion is sadly mistaken," said New York Sen. Charles Schumer, one of several Democrats who used Senate speeches to criticize Alito.

"There are too many questions still to be answered, too many doubts still to be alleviated to say that this nomination is a slam dunk," Schumer said.

Conservative Republicans came to Alito's defense, with some committing their votes more than a month before his Jan. 9 confirmation hearing.

Others are warning Democrats not to think about using a filibuster to stop the federal appeals court judge from succeeding retiring Justice Sandra Day O'Connor. She has provided pivotal votes on contentious issues, including abortion, during her 24 years on the high court.

"Even a suggestion that he doesn't deserve an up-or-down vote is outrageous," said Sen. Kay Bailey Hutchison, R-Texas.

Alito has gotten generally positive reviews from senators since the White House announced his nomination on Halloween as the replacement for Harriet Miers. The White House counsel withdrew her nomination after criticism from conservative commentators about her lack of judicial experience.

Democrats and Republicans have praised Alito's knowledge, intelligence and his willingness to answer their questions during the private meetings.

But three influential Democrats — Minority Leader Harry Reid of Nevada, liberal stalwart Edward Kennedy of Massachusetts and Schumer, head of the Democratic Senatorial Campaign Committee — said in Senate speeches that they had "significant concerns" about Alito's nomination.

"A picture of Sam Alito is emerging that may explain why the extreme right-wing is popping champagne corks," said Reid. Alito, he said, is "one of the most conservative federal judges in the country."

Some senators are concerned that that Alito, along with recently confirming Chief Justice John Roberts, would move the Supreme Court to the right and perhaps overturn the landmark 1973 Roe v. Wade decision that established abortion rights.

Alito, in a 1985 application to be deputy assistant attorney general, promoted his anti-abortion work in the solicitor general's office. That was work, Alito said at the time, "in which I personally believe very strongly."

Alito, a judge for the past 15 years on the 3rd U.S. Circuit Court of Appeals, has tried to distance himself from the document this week, telling senators that he is older and wiser.

"A lot of things have happened since 1985," the chairman of the Judiciary Committee told the U.S. Chamber of Commerce. "For one thing, Judge Alito has said that he believes in a right of privacy in the Constitution," said GOP Sen. Arlen Specter of Pennsylvania, who generally has supported abortion rights.

"Judge Alito told me that he understands that the law governing the right to abortion has become more settled over the last 20 years, including the Supreme Court's Casey decision in 1992 where the Court expressly upheld Roe," said Sen. Olympia Snowe, a moderate Maine Republican.

Democrats say they plan to question Alito closely on the issue.

"He said he was 35 when he wrote that," said Democratic Sen. Joseph Biden of Delaware, who met with Alito on Wednesday.

"I pointed out that I had been a senator five years when I was 35, and no one says to me what you said in 1974 as a senator we can forget," Biden said.

Snowe said Alito told her he had a "deep-seated respect for the doctrine of precedent." But Biden said Alito in their meeting "acknowledged that no Supreme Court justice is bound by any precedent."

Conservative Republicans have welcomed Alito's nomination. Already some lawmakers, including GOP Sens. Wayne Allard of Colorado and Jim DeMint of South Carolina, have said they will vote to confirm Alito.

"I'm excited about defending and supporting this nominee, and am convinced he will be a great addition to the Supreme Court," DeMint said Wednesday, with the judge sitting quietly at his side.

Reid pointed out that conservatives -- not liberals -- forced Miers' withdrawal before her confirmation hearing, and he said Republicans such as Senate Majority Leader Bill Frist of Tennessee should not threaten Democrats with banning judicial filibusters.

"The majority leader should put his sword back in its sheath and let the Senate move forward on this nomination without idle threats," said Reid, who plans to meet with groups opposed to Alito on Thursday.