WASHINGTON, June 9 — While the Libyan leader, Col. Muammar el-Qaddafi, was renouncing terrorism and negotiating the lifting of sanctions last year, his intelligence chiefs ordered a covert operation to assassinate the ruler of Saudi Arabia and destabilize the oil-rich kingdom, according to statements by two participants in the conspiracy. Those participants, Abdurahman Alamoudi, an American Muslim leader now in jail in Alexandria, Va., and Col. Mohamed Ismael, a Libyan intelligence officer in Saudi custody, have given separate statements to American and Saudi officials outlining the plot. Mr. Alamoudi, has told Federal Bureau of Investigation officials and federal prosecutors that...