Washington ? Vice President Dick Cheney will be called to testify on behalf of his former chief of staff in the CIA leak case, defense attorneys said Tuesday, ending months of speculation about what would be historic testimony.

“We’re calling the vice president,” attorney Ted Wells said in court. Wells represents defendant I. Lewis “Scooter” Libby, who is charged with perjury and obstruction.

Presidential historians and legal experts said they were unaware of a sitting vice president testifying at a criminal trial. Several presidents have given testimony in court cases, including Bill Clinton and Gerald Ford.

Ohio State University law professor Peter Shane said Cheney’s appearance also is unusual because of his aggressive efforts in other matters to protect the executive office from being forced to disclose details of its deliberative process or inner workings.

Cheney waged a lengthy legal battle to avoid having to release information about energy executives and others who participated in a task force he created to help shape the administration’s energy policy.

William Jeffress, another of Libby’s attorneys, would not say whether Cheney is under a subpoena to testify. Issuing a court order to a sitting vice president could raise separation-of-powers concerns, but Jeffress said it was not an issue.

“We don’t expect him to resist,” Jeffress said.

Special Prosecutor Patrick Fitzgerald, who said last week said he did not expect the White House to challenge his witnesses, said Tuesday he did not plan to call Cheney.

Lawyers for Vice President Dick Cheney's former top aide told a federal judge Tuesday that the defense plans to call the vice president to testify and expects him to cooperate. That would make Cheney, above, the first sitting vice president to testify in a criminal case, presidential historians and legal experts say.

Wells immediately said he would.

“That settles that,” Fitzgerald said.

Neither Jeffress nor Wells would say whether they expect Cheney to testify in the courtroom or offer videotaped testimony to avoid infringing on the separation of powers.

“We’ve cooperated fully in this matter and will continue to do so in fairness to the parties involved,” said Lea Anne McBride, a spokeswoman for the vice president. “As we’ve stated previously, we’re not going to comment further on a legal proceeding.”

Libby is accused of lying to investigators about what he told reporters regarding former CIA operative Valerie Plame. Plame’s identity was leaked to reporters around the time that her husband, former Ambassador Joseph Wilson, publicly criticized the Bush administration’s prewar intelligence on Iraq.

Libby says he was focused on more important issues – including terrorism, Iraq and nuclear proliferation – and didn’t remember his conversations regarding Plame.

Cheney could bolster that argument by testifying about the many other larger issues Libby was responsible for.