WASHINGTON (AP) – Congressional Democrats investigating the firings of eight Federal prosecutors pressed ahead with their probe Wednesday, interviewing one of Attorney General Alberto Gonzales’ top aides and serving notice that the administration best come forth with more answers.

On both sides of the Capitol, lawmakers kept up the pressure on Mr. Gonzales, who has disappeared from public view as he prepares to tell his story to a Senate panel next Tuesday.

Behind closed doors Wednesday, the Senate Judiciary Committee interviewed Bill Mercer, acting associate attorney general whose name appears frequently in Justice Department e-mails that document the plans to fire the prosecutors over the winter.

On the House side, Judiciary Committee Chairman John Conyers on Tuesday issued a subpoena for hundreds of Justice Department documents that must be turned over by next Monday, less than 24 hours before Gonzales is scheduled to explain his role in the firings to the Senate Judiciary Committee in what is widely considered a last chance to save his job.

There’s more where that came from, as the White House tries to balance its stated desire to be forthcoming about the firings with its fierce protection of internal documents.

The Senate panel is expected to keep up the pressure by authorizing subpoenas Thursday to compel cooperation from White House officials. On Friday, the House and Senate committees will again question Kyle Sampson, Mr. Gonzales’ former chief of staff who quit over the scandal. That session, unlike Mr. Sampson’s public testimony two weeks ago, will not be open to the public, according to an official close to the investigation.

Unlike Mr. Conyers, Senator Leahy of Vermont, Democrat of Vermont and the chairman of the Senate committee, has not issued any subpoenas in the firings investigation. But Mr. Leahy sent a letter to Justice requesting the blacked out, or redacted, information – often a prelude to issuing a subpoena.

It all adds up to relentless pressure on an administration that for six years of Mr. Bush’s tenure operated with virtually no oversight from the Republican-controlled Congress.

No longer.

The firings of prosecutors from California to Arkansas and Mr. Gonzales’ shifting explanations have produced calls from some lawmakers of both parties for a new attorney general.

Some, like Democratic Senator Feinstein, Democrat of California – home to two of the dismissed prosecutors – say Mr. Gonzales lied in private conversations and have demanded that he step down. Others, such as Senator Sununu, Republican of New Hampshire, have called for Mr. Gonzales to resign because of the accumulated damage from the firings and other Justice problems, like excessive use of secret national security letters in terrorism cases.

Still others, such as Senator Specter, Republican of Pennsylvania, have noted that Justice Department e-mails make clear that Mr. Gonzales’ chief of staff at one point advocated using a new provision in the USA Patriot Act to install federal prosecutors without Senate confirmation. Nevertheless, Mr.Specter, the top Republican on the Judiciary Committee, appealed for open minds until Mr. Gonzales has a chance to tell his story.

Despite the pressure and a challenge facing Gonzales that some see as insurmountable, Mr. Bush is standing by his longtime friend from Texas.

“I think the Justice Department has been working very hard to be fully responsive to the request, as the president asked them to do,” White House spokeswoman Dana Perino said Tuesday.

Democrats disagree, complaining about the redacted portions of more than 3,000 documents released by Justice last month.

“We have been patient in allowing the department to work through its concerns regarding the sensitive nature of some of these materials,” Mr. Conyers wrote Mr. Gonzales in a letter accompanying the subpoena. “Unfortunately, the department has not indicated any meaningful willingness to find a way to meet our legitimate needs.”

Responding, Justice spokesman Brian Roehrkasse stopped short of saying the department would fight the subpoena. But he said the department has not released them because of legal concerns about violating privacy rights of people mentioned in the documents.

“Much of the information that the Congress seeks pertains to individuals other than the U.S. attorneys who resigned,” Mr. Roehrkasse said. “Because there are individuals’ privacy interests implicated by publicly releasing this information, it is unfortunate that Congress would choose this option.”

He added: “In light of these concerns, we will continue to work closely with congressional staff and we still hope and expect that we will be able to reach an accommodation with the Congress.”

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Associated Press writers Lara Jakes Jordan and Ben Feller contributed to this report.