AT&T has been ordered to propose still lower long-distance telephone rates to go into effect June 1 or explain why it can't, the Federal Communications Commission said . . . Alaska Airlines and its clerical, office and passenger service employees approved a new contract that includes an overall 20% reduction in compensation . . . The U.S. Comptroller of the Currency has given troubled First Oklahoma Bancorporation until June 16 to raise new capital, company officials reported . . . Coca-Cola USA said it will introduce an iced-tea product, to be called Refresh, in restaurants starting in July . . . Security Pacific Information Systems, a unit of Security Pacific Corp., has signed a four-year, multimillion-dollar agreement to provide complete data-processing support to Empire Savings of Denver.