President Bush's top legal aides were to tell congressional Democrats on Friday whether and under what conditions they would allow high-level White House officials, including Rove, to testify under oath in the inquiry.
Subpoenas could come as early as next week.
E-mails released this week, including a set issued Thursday night by the Justice Department, appear to contradict the administration's assertion that Mr. Bush's staff had only limited involvement in the firings of eight U.S. attorneys, which Democrats have suggested were a politically motivated purge.
Each new piece in the rapidly unfolding saga of how the prosecutors came to be dismissed has made it more difficult for the White House to insulate itself from the controversy.
The latest e-mails between White House and Justice Department officials show that Rove inquired in early January 2005 about firing U.S. attorneys.
The one-page document, which incorporates an e-mail exchange in January 2005, also indicates Gonzales was considering dismissing up to 20 percent of U.S. attorneys in the weeks before he took over the Justice Department.
In the e-mails, Gonzales' top aide, Kyle Sampson, says that an across-the-board housecleaning "would certainly send ripples through the U.S. attorney community if we told folks they got one term only." But it concludes that "if Karl thinks there would be political will to do it, then so do I."
Sampson resigned this week over the prosecutors' firings and the Justice Department's misleading of Congress about the process.
The e-mails "show conclusively that Karl Rove was in the middle of this mess from the beginning," said Sen. Charles Schumer, D-N.Y. "Every time new information comes out, it proves that the White House was not telling the truth."
Earlier Thursday, Rove said the controversy was being fueled by "superheated political rhetoric," adding that there was no similar uproar when President Clinton dismissed all 93 U.S. attorneys at the beginning of his first term.
"We're at a point where people want to play politics with it. That's fine," Rove told students at Troy University in Alabama.
The White House said the e-mails don't undercut their account of Rove's involvement in the matter. Rove has a "vague recollection" that the idea to fire all 93 U.S. attorneys at the start of Mr. Bush's second term came from then-White House Counsel Harriet Miers, deputy press secretary Dana Perino said.
"He thought it was a bad idea and would be unwise," Perino said.
The Senate Judiciary Committee has subpoenaed Justice Department officials in the probe. The panel will vote March 22 on subpoenas for Rove, Miers and her deputy, William K. Kelley.
More Republicans called for his ouster, and one Republican strategist close to the White House told CBS News
Congressman Dana Rohrbacher became the latest Republican to say Gonzales should go, reported CBS News chief White House correspondent Jim Axelrod.
"Even for Republicans this is a warning sign … saying there needs to be a change," said Rohrbacher. "Maybe the president should have an attorney general who is less a personal friend and more professional in his approach."
Sen. John Sununu of New Hampshire has also publicly urged Mr. Bush to fire Gonzales. Another GOP lawmaker not ready to speak out publicly, said Thursday he planned to call next week for Gonzales to step down. And Sen. Gordon Smith, R-Ore., said Thursday that Gonzales had lost the confidence of Congress.
Other Republican lawmakers are trying to quell the uproar until they hear from Gonzales and his aides.
"Let's give them a chance to respond before we get tough," said Sen. Arlen Specter of Pennsylvania, the senior Judiciary Committee Republican. "I'm prepared to get tough, but I want to get tough with a basis for doing so."
It's customary for new presidents to bring in their own team of prosecutors when they take office. Democrats say the Bush administration singled out some of its own nominees because they chafed at the president's priorities and Republican efforts to influence political corruption investigations.
"Eight U.S. attorneys who did not play ball with the political agenda of this administration were dropped from the team," said Senate Democratic Whip Dick Durbin of Illinois. "We have a right to ask what that political agenda was and whether or not it was a reasonable firing and dismissal."
Mr. Bush on Wednesday defended the firings but criticized how they were explained to Congress. The president said he still had confidence in the attorney general but implied that his support was conditioned on Gonzales patching things up with lawmakers.