The federal government agreed yesterday to pay $508 million, the largest award ever in an employment discrimination case, to end a lawsuit filed 23 years ago by hundreds of women who said they were denied jobs and promotions at the U.S. Information Agency and Voice of America. The agreement ends a tortured legal battle that began after Carolee Brady applied for a job as a USIA magazine editor, only to be told that managers were seeking a man. Brady’s complaint ballooned into a class action lawsuit with roughly 1,100 women alleging they too lost opportunities because of their gender. Many said they were bypassed in favor of men with far less experience who scored poorly on hiring tests.