The second-day session grew contentious as Democrats displayed frustration with Roberts' answers and his oft-repeated explanation that he couldn't address some issues that could come before the Supreme Court with him as chief justice.
"Go ahead and continue not to answer," Sen. Joe Biden, D-Del., told the nominee at one point.
Later, Biden interrupted Roberts and, when criticized by the Judiciary Committee chairman, said, "His answers are misleading, with all due respect."
"Wait a minute! Wait a minute! They may be misleading but they are his answers," said Sen. Arlen Specter, R-Pa., the chairman.
"With respect they are my answers and with respect, they are not misleading," Roberts responded.
Senators questioned President Bush's choice to succeed the late William H. Rehnquist on abortion, privacy, voting rights and the balance of power between the branches of government. Roberts frequently answered through the prism of legal precedent but declined to address specifics.
The heart of the abortion ruling is "settled as a precedent of the court, entitled to respect under principles of stare decisis," the concept that long-established rulings should be given extra weight, Roberts said.
Still, review and revisions have been the hallmark of the high court on issues from integration to gay rights, and Roberts indicated that groundbreaking cases can draw a second look.
"If particular precedents have proven to be unworkable, they don't lead to predictable results, they're difficult to apply, that's one factor supporting reconsideration," Roberts said.
If confirmed, the 50-year-old Roberts would be the youngest chief justice in 200 years, with the power to shape the high court for decades. Democrats and Republicans see no major obstacles to his winning Senate approval and joining the other justices when the new term begins Oct. 3.
In his answers on abortion, Roberts focused on a 1992 Supreme Court ruling in Casey v. Planned Parenthood, referring to that as a precedent-setting case in addition to the 1973 Roe v. Wade ruling.
In the Pennsylvania case, the Supreme Court voted 5-4 to uphold the core holdings of Roe v. Wade and ban states from outlawing most abortions. The court said states could impose restrictions on the procedure that do not impose an "undue burden" on women.
"It reaffirmed the central holding in Roe v. Wade," Roberts said.
After the morning session, Sen. Charles Schumer, D-N.Y., characterized Roberts' answers: "There's precedent and then there's overruling precedent. That's pretty much his answer on Roe."
Bush originally nominated Roberts to succeed Justice Sandra Day O'Connor, the court's crucial swing vote who announced her plans to retire in July. Within days of Rehnquist's death on Sept. 3, Bush tapped Roberts to be chief justice.
Democrats pressed the appellate judge about his writings on civil rights while a young lawyer in the Reagan administration two decades ago. Sen. Edward M. Kennedy, D-Mass., described some of those writings on voting rights as a "narrow, cramped and mean-spirited view" that failed to show a full appreciation of discrimination.
Under questioning from Kennedy, Roberts said that he had no problem with the 1965 Voting Rights Act. "The constitutionality has been upheld, and I don't have any issue with that."
That failed to assuage Kennedy, who spoke critically and at length about Roberts' writings. Kennedy was interrupted several times Specter, who told him to let Roberts speak.
The nominee dismissed any suggestion that his Catholic faith would influence his decisions if he were confirmed. The Roman Catholic Church strongly opposes abortion.
"There's nothing in my personal views based on faith or other sources that would prevent me from applying the precedent of the court faithfully under the principles of stare decisis," Roberts said.
Stare decisis is Latin for "to stand by a decision" and legally translates into the doctrine that says courts are bound by previous decisions, or precedents, particularly when a case has been decided by a higher court.
Despite that principle, the current Supreme Court has been willing to revisit and overrule previous court decisions, on issues such as gay rights and the death penalty.
Questioned about rights of privacy, the appellate judge cited several amendments in the Bill of Rights and said, "The court has explained that the liberty protected is not limited to freedom from physical restraint."