The president and chief executive officer of Prime Healthcare Services has resigned, leaving as FBI agents are questioning former employees about the firm's billing practices and state legislators prepare to question the company's attorney in a Los Angeles hearing tomorrow regarding hospital reimbursement. The resignation was confirmed today by Prime, which owns Alvarado Hospital in San Diego and Paradise Valley in National City. Lex Reddy, who is the brother-in-law of Prime's owner and board chairman, Dr. Prem Reddy, began working as a clerk for Prem Reddy's medical group in 1995. During the last 11 years, Prem Reddy, a cardiologist, built the 16-hospital Prime chain with Lex Reddy at the helm. According to a company statement, Prem Reddy will take over as interim chief executive. No reason was given for the departure.