Jim Letten, the United States attorney for New Orleans, recused himself from the case involving four men arrested last week on charges of interfering with the phones in Senator Mary L. Landrieu’s office. Mr. Letten said that after consulting with Justice Department officials, and “in consideration of various relevant factors,” he was allowing his first assistant attorney to handle the case. Ms. Landrieu, a Democrat, has requested that Mr. Letten, who was appointed by President George W. Bush, be reappointed. In addition, one of the four men arrested is the son of the acting United States attorney for the Northern District of Louisiana.