WASHINGTON — Mayor Giuliani’s strong criticism of a federal judge’s 30-month prison sentence for I. Lewis Libby Jr. signals a departure for the Republican presidential hopeful and former prosecutor, who had previously shied away from speculating about the case.

In response to a question at the GOP debate Tuesday night, Mr. Giuliani called the punishment “grossly excessive,” a position that aligns him with many conservatives but prompted skepticism from some legal and political scholars, who said it was at odds with Mr. Giuliani’s record as an aggressive prosecutor and a tough-on-crime mayor.

“I think the sentence was way out of line,” Mr. Giuliani said when asked if a presidential pardon would be appropriate for Libby, a former chief of staff to Vice President Cheney who was convicted of lying to a grand jury and the FBI and obstructing a federal investigation into the leaked identity of a CIA officer.

“I mean, the sentence was grossly excessive in a situation in which, at the beginning, the prosecutor knew who the leak was, and he knew a crime wasn’t committed,” the former mayor added, saying that Judge Reggie Walton’s sentence “argues more in favor of a pardon, because this is excessive punishment.”

Mr. Giuliani was considerably more circumspect about the case, and a potential pardon, following Libby’s conviction in March. “You certainly shouldn’t speculate about it while a criminal case is ongoing,” he told reporters then.

The Libby question split the GOP field Tuesday night. Senator McCain of Arizona said the president should wait for the appeals process to play out, while Mitt Romney railed against the special prosecutor, Patrick Fitzgerald, saying he “clearly abused prosecutorial discretion” in pursuing perjury and obstruction of justice charges against Libby when he knew the former White House aide was not the original source of the leak. “He went on a political vendetta,” Mr. Romney said.

Mr. Giuliani’s campaign declined to elaborate on his views yesterday, but a spokeswoman, Maria Comella, said it was correct to characterize his statement as a criticism of the prosecution.

The former mayor has experience on both sides of the issue. He ran President Reagan’s pardon office as an associate attorney general in the 1980s and prosecuted thousands of cases as U.S. attorney for the Southern District of New York later in the decade.

His assault drew criticism from some legal experts, who pointed out that Judge Walton had followed federal sentencing guidelines in handing down the punishment, which included a $250,000 fine. Judge Walton, who was appointed to the federal bench by President Bush, is known for giving tough sentences.

“The statement is really unfair to the court,” a former U.S. attorney for the District of Columbia, Roscoe Howard Jr., said of Mr. Giuliani. “To me it’s a statement clearly aimed at voters leaning Republican.”

“It’s unfortunate,” Mr. Howard said. “It’s just unfortunate.”

Mr. Giuliani also drew criticism from a rival GOP contender with a background in the law, James Gilmore, who served as both a prosecutor and attorney general of Virginia before becoming governor of the state. Mr. Gilmore said during the debate that a pardon of Libby would be inappropriate. “I’m steeped in the law,” he said. “I wouldn’t do that.”

In an interview yesterday, Mr. Gilmore acknowledged that he hadn’t followed the Libby case closely, but he stood by his statement and said he had seen nothing to suggest that justice was not served. “I could have pandered and won some friends someplace,” he said.

Judge Walton sentenced Libby within the range recommended by the prosecution. He rejected arguments from the defense that Libby should be spared prison because of his public service. The defense also urged the judge to use different sentencing guidelines that would have resulted in less time, arguing that it was warranted because the prosecution had not proven the existence of the “underlying offense,” in this case the leak itself.