Justice Department officials said Monday that they had only learned recently about Mr. Sampson’s extensive e-mail and memos with Ms. Miers about the prosecutors. The communications were discovered Thursday when Mr. Sampson turned over the material to officials who were assembling documents in response to Congressional requests.

The documents did not provide a clear motive for the firings. Some suggested that department officials were dissatisfied with specific prosecutors, but none cited aggressive public corruption inquiries or failure to pursue voter fraud cases as an explicit reason to remove them.

On Dec. 4, 2006, three days before the dismissals, Mr. Sampson sent an e-mail message to the White House with a copy to Ms. Miers outlining plans to carry out the firings

“We would like to execute this on Thursday, Dec. 7,” Mr. Sampson wrote. Because some United States attorneys were still in Washington attending a conference, he planned to postpone telling them they were being fired. He wrote, “We want to wait until they are back home and dispersed to reduce chatter.”

Mr. Sampson predicted that dismissals might stir debate. “Prepare to Withstand Political Upheaval,” he wrote in describing what to expect as a result of the firings. “U.S Attorneys desiring to save their jobs aided by their allies in the political arena as well as the Justice Department community, likely will make efforts to preserve themselves in office. You should expect these efforts to be strenuous.”

Mr. Rove’s role in expressing concerns about prosecutors had emerged in recent days. The White House acknowledged Sunday that Mr. Rove had passed on complaints to Mr. Gonzales and Ms. Miers about David C. Iglesias, who was dismissed as the United States attorney in New Mexico. Mr. Rove’s role surfaced after the McClatchy Newspapers reported that a Republican Party official in New Mexico had complained to Mr. Rove in 2005 and again a year later about Mr. Iglesias’s failure to indict Democrats in a voter fraud investigation.

Concern about voter registration fraud turned political in several states in 2004 where there were close elections, including some lost narrowly by Republican candidates. In New Mexico, for example, complaints from Republicans poured in, including some from Representative Heather Wilson and Mr. Domenici, after President Bush narrowly lost to Senator John Kerry that year, and some voters claimed that they had been unable to participate because someone had illegally voted on their behalf. The narrow loss by a Republican in the Washington State governor’s race in 2004 produced similarly politically pointed charges.