Supreme Court nominee Samuel Alito, second from right, prepares to testify on Capitol Hill

President Bush's nominee to the U.S. Supreme Court, Judge Samuel Alito, says he would be an impartial justice if confirmed to the high court.  Democrats are vowing tough questioning of Judge Alito when testimony begins in Senate Judiciary Committee hearings Tuesday. 

In a brief opening statement to the Judiciary Committee Monday, Judge Alito said he would be a fair justice if the Senate confirms him to the Supreme Court.  He said he made a similar pledge when he became an appeals court judge 15 years ago.

"I swore that I would administer justice without respect to persons, that I would do equal right to the poor and to the rich, and that I would carry out my duties under the Constitution and the laws of the United States," said Mr. Alito.  "That is what I have tried to do to the very best of my ability for the past 15 years.  If I am confirmed, I pledge to you that that is what I will do on the Supreme Court."

If confirmed, Judge Alito would succeed retiring Justice Sandra Day O'Connor, a centrist, who often cast the deciding vote in five-to-four rulings in controversial cases on the deeply divided court.  Sometimes she sided with the more conservative justices, while other times she voted with the more liberal members of the bench.

Senate Democrats fear the conservative Judge Alito could tilt the ideological balance of the court to the right.

They are particularly concerned by the nominee's record on the limits of presidential power and on abortion rights.

They cite his writings and rulings as a judge and when he worked as a lawyer in the Reagan administration in support of expanded powers of the executive.  In the wake of revelations that President Bush ordered without warrants eavesdropping on Americans suspected of terrorist ties, critics find Judge Alito's arguments troubling.

The issue is expected to dominate the hearings.   Senator Charles Schumer, a New York Democrat, offered a preview of the line of questioning he will pursue.

"We need to know, when a president goes too far, will you be a check on his power, or will you issue him a blank check to exercise whatever power alone he thinks appropriate?" he asked.

Another key issue at the hearings is expected to be abortion. 

Critics are concerned Judge Alito may try to undermine or overturn the 1973 Supreme Court decision known as Roe versus Wade, which legalized abortion.   They cite a 1985 memo Judge Alito wrote as part of a job application with the Reagan administration in which he argued there was no constitutional right to abortion.

"I am also concerned with the impact you could have on women's rights, specifically, a woman's right to choose," said Senator Dianne Feinstein, a California Democrat..

Judge Alito's Republican supporters argue he is a fair-minded, mainstream conservative, who will put aside his personal views in deciding cases.

Senator Jon Kyl, an Arizona Republican, says Judge Alito is well qualified to serve on the high court. "You have more judicial experience than any Supreme Court nominee in more than 70 years," said Mr. Kyl.

Senators are expected to question Judge Alito Tuesday and Wednesday.  Some 30 witnesses are to testify in support of or against the nomination Thursday.

Despite likely opposition from Democrats, Judge Alito is expected to be confirmed by the Republican-led Senate later this month.