Why Not Have Gonzales Testify Under Oath?

CNN reports:

The hearing began with a sudden and sharp partisan dispute when Senate Judiciary Committee Chairman Arlen Specter ruled that Gonzales did not have to be sworn in to testify. After Democrats strongly objected and demanded a roll-call vote, Republicans prevailed and the attorney general did not testify under oath.

Before one asks why not, let’s see what he has been reported to have said to the Senate committee:

“The terrorist surveillance program is necessary, it is lawful and it respects the civil liberties we all cherish,” Gonzales said … Gonzales told the committee that the program is limited to communication between someone in the U.S. and someone in a foreign nation; triggered when a NSA professional beliefs one of the parties is tied to al Qaeda … Gonzales responded that he was asked whether the president could authorize surveillance that violated law. “That has not occurred”, he said.

My question sort of answers itself – it would not be prudent for the Attorney General to have lied under oath, would it?