US senators grilled Judge Samuel Alito, the Supreme Court nominee, on Tuesday on his views on civil rights, the power of the presidency and abortion but they appeared to land no obvious knock-out blow against the imperturbable nominee.

After several hours of questioning by the Senate judiciary committee, Democrats appeared to have gained no new ammunition to defeat Mr Alito’s nomination, which is expected to be approved by the full Senate later this month.

Mr Alito moved quickly to allay fears that he is a conservative ideologue bent on overturning Roe v Wade, the Supreme Court’s 1973 precedent legalising abortion, and that he is committed to theories of civil rights and executive power that would dramatically alter the way the top US court rules in these areas.

He immediately stressed the importance of respecting precedents such as Roe v Wade. He repeated several times that most issues that come before the court were covered by precedents and that judges should be guided by prior rulings in approaching current issues.

“There needs to be a special justification for overruling a prior precedent,” he said.

If the court decided to revisit Roe, he would “keep an open mind” in spite of the fact that, as a lawyer in the Reagan Justice Department in the 1980s, he advocated overturning the ruling.

Senators spent much of the session questioning the nominee on his views on the power of the presidency in wartime, including President George W. Bush’s decision to allow spying on Americans without a court order.

Mr Alito refused to comment directly on the issue, since he said it was likely to end up before the court on which he hopes to sit. But he stressed the importance of a Supreme Court precedent from the Korean war, which limits the power of the president in wartime.

Asked whether he agreed with a statement by Justice Sandra Day O’Connor – the justice he hopes to replace – that the constitution did not give the president a “blank cheque” of power during wartime, he replied with an emphatic “yes”.

“That’s a very important principle,” Mr Alito said. “Our constitution applies in times of peace and at times of war and our constitution protects the rights of Americans at all times.’”

Mr Alito faced the toughest questioning on the issue of discrimination. Senator Patrick Leahy, the top Democrat on the committee, demanded that Mr Alito explain how he could have joined a group in the 1970s that opposed the admission of women and minorities to Princeton University. He said he had no memory of joining the group but believed he had done so because of its views on the military, not on minorities.

He outlined a narrow view of the role of judges in society, saying courts should enforce policy decisions made by the legislature and the executive without trying to make policy themselves.

“Courts have an important role to play but it is a limited role. It’s important for them … not to try to do somebody else’s job.”