WASHINGTON - Congress sought cooperation from one Justice Department official and prepared to put the agency's former White House liaison under oath in a widening investigation into the politics of the department's decision-making.

The Senate Judiciary Committee asked Bradley Schlozman, a former senior civil rights attorney and U.S. attorney, to speak with investigators. The Justice Department, meanwhile, said it wouldn't try to prevent Congress from granting immunity to White House liaison Monica Goodling if she testified before a committee.

Lawmakers want to talk to Schlozman and Goodling as part of an inquiry into whether Justice played politics with the hiring and firing of department officials. The inquiry began as a question about whether U.S. attorneys - presidential appointees who serve as the top federal law-enforcement officials in their state districts - were fired for political reasons.

It has grown into an investigation of whether the department let politics affect criminal investigations and whether officials made employment decisions for political reasons.

Lawmakers want to question Schlozman, who now works for the Executive Office for United States Attorneys, about a voter-fraud lawsuit he filed against Missouri in the lead-up to the 2006 election. Committee members said they wanted to know whether Schlozman's predecessor was forced out for not endorsing that lawsuit, which was ultimately dismissed.

Senate Judiciary Chairman Patrick J. Leahy (D., Vt.) wrote in a letter co-signed by the top Judiciary Republican, Arlen Specter (R., Pa.): "The Committee would benefit from hearing directly from you in order to gain a better understanding of the role voter fraud may have played in the administration's decisions to retain or remove certain U.S. attorneys."

The letter asked Schlozman to voluntarily submit to interviews and testimony and to provide documents to the committee.

Justice spokesman Dean Boyd said politics did not influence decisions about whether to bring a case. The department, he said, "brings its civil actions and criminal prosecutions based on evidence, not on politics. We expect U.S. attorneys to bring election and voter-fraud cases where evidence of such fraud exists."

The department is conducting an internal review of the firings of U.S. attorneys and other decisions. As part of that investigation, it is reviewing whether Goodling sought to place Republicans as frontline prosecutors in state U.S. attorney districts.

Lawmakers want to question Goodling, but, with no promise of immunity, she has refused. In a letter to House Judiciary Committee Chairman John Conyers Jr. (D., Mich.), the department said it would prefer not to see an immunity deal.

"However, we understand the committee's interest in obtaining Ms. Goodling's testimony," the letter said. "Therefore, after balancing the significant public interest against the impact of the committee's actions on our ongoing investigation, we will not raise an objection or seek a deferral."

The letter was signed by Inspector General Glenn Fine and H. Marshall Jarrett, counsel to the Office of Professional Responsibility.

Committee lawyers must now send an immunity request to a federal judge for approval. Once that deal is approved, Goodling would face a contempt order if she refused to testify. Her lawyer, John M. Dowd, said yesterday that she would testify under such a deal.

"She'll be honest and clear," Dowd said, "and she'll work very hard to answer all questions."