Dick Cheney will be called to testify at the perjury and obstruction trial of his former chief of staff, in what would be a historic appearance by a vice president in a criminal prosecution, lawyers said Tuesday.

The decision by I. Lewis "Scooter" Libby's lawyers to call Cheney as a witness in the federal trial scheduled to begin here Jan. 16 ends months of speculation about the role senior White House officials would play.

It also sets the stage for a dramatic appearance that could offer insight into Cheney's relationship with his top aide, and for a cross-examination by special prosecutor Patrick J. Fitzgerald that could lay bare how the Bush administration responded to its critics. ...

In 1988, Vice President George H.W. Bush testified to investigators in the Iran-Contra arms-for-hostages probe, but his testimony was never used.

By contrast, a number of presidents have participated in trials over the years, often by videotape.

President Clinton gave videotaped testimony in a criminal trial involving two former business partners in the Whitewater land deal.

President Ford gave a videotaped deposition in the trial of Lynette "Squeaky" Fromme, who was convicted of trying to assassinate him.

And President Carter provided videotaped testimony in a grand jury investigation of financier Robert Vesco.