Sonia Sotomayor sped toward confirmation as the first Hispanic justice Thursday, encouraged by Republican promises of a quick vote and cheered on by a Democratic senator's challenge to take on the U.S. Supreme Court's conservative wing when she arrives.

"Battle out the ideas that you believe in, because I have a strong hunch that they are closer to the ones that I would like to see adopted by the court," Sen. Arlen Specter, a Republican turned Democrat, told Sotomayor.

Even two of her Republican critics called the 55-year-old appeals court judge's rulings "mainstream" -- noteworthy concessions for President Obama's first high court nominee.

If confirmed, Sotomayor would become the first justice appointed by a Democratic president in 15 years, and the hearings were as much a prelude for future Supreme Court fights as a battle over the judge herself. Republicans repeatedly criticized Obama's past assertion that he wanted a justice with "the quality of empathy," and Sotomayor disavowed Obama's statement as a senator that some decisions would be determined by "what is in a judge's heart."

Republicans, expressing concern that she would bring bias to the court, brought in Frank Ricci, a white New Haven, Connecticut, firefighter whose reverse discrimination claim was rejected by Sotomayor and two other appeals court judges, to testify against her. He complained that the ruling showed a belief "that citizens should be reduced to racial statistics," but he did not say her nomination should be rejected.

Her panel's ruling was overturned last month by the Supreme Court she hopes to join.

Four days of confirmation hearings concluded just before nightfall Thursday after an afternoon of testimony from 30 other witnesses, including Sotomayor's mentors and supporters as well as critics who voiced concerns about how she'd rule on matters involving abortion, gun and property rights.

Her elevation all but assured, Sotomayor took few risks during her own testimony, repeatedly sidestepping questions on hot-button issues like guns and abortion rights and defending speeches that have been faulted as showing bias.

The Judiciary Committee's top Republican, Jeff Sessions, declared he still had "serious concerns" about Sotomayor, but said he would not support any attempt to block a final vote on confirmation and did not foresee any other Republican doing so. A committee vote on confirming her is expected late this month.

Sotomayor has overwhelming if not unanimous support among the Senate's 58 Democrats and two independents -- and is likely to win a number of votes among the 40 Republicans as well.

Her confirmation hearings were fraught with racial politics that created a dilemma for Republicans, who stepped carefully during their tough questioning of Sotomayor -- eager to please their conservative base but wary of alienating Hispanics, the fastest-growing voting demographic.

They pressed Sotomayor repeatedly on her 2001 statement that she hoped a "wise Latina" would usually rule better than a white male, drawing expressions of regret from the nominee, who said the words had been taken out of context and misunderstood.

In four days of testimony -- she gave a brief opening statement on Monday -- Sotomayor presented herself as a staunch and impartial defender of the law. She rarely strayed from a script replete with pledges to put her feelings and prejudices aside when she rules.

"I regret that I have offended some people," Sotomayor said Thursday, confronted by Sen. Lindsey Graham, a Republican, about comments he said "bug the hell out of me."

Sotomayor appeared to have reassured at least some Republicans. Graham described her judicial record as "generally in the mainstream" and said he thought she would keep an open mind on gun rights. Graham, who has said previously he might vote to confirm Sotomayor, said she was "not an activist."

Another Republican, Sen. John Cornyn , also called Sotomayor's rulings "pretty much in the mainstream," although he said her assertions of impartiality at the hearings were strikingly at odds with her past remarks.

Nearby in the Capitol, Sen. Jim Bunning, a Republican, announced he would oppose Sotomayor, saying she was "unsuitable" for the court.

The National Rifle Association announced it would oppose Sotomayor, saying she held a "hostile view" of the Second Amendment right to keep and bear arms, although a spokesman declined to say whether the group would include her confirmation vote in its ratings of lawmakers. The NRA's closely watched "scores" weigh heavily on lawmakers in both parties, since they're a powerful motivator for politically active gun rights supporters.

Committee chairman Patrick Leahy, a Democrat ., said he expected Sotomayor would win some Republican votes.