Legislation recently approved by Congress without benefit of committee hearings is expected to have a major impact on federal sentencing. One provision of the law requires mandatory life sentences for those twice convicted of federal sex offenses. Another provision would mandate an eventual reduction in the opportunity of judges to impose sentences below the guidelines set by the U.S. Sentencing Commission. A third would allow the Justice Department to monitor the rates at which individual judges impose sentences below the guidelines. In a very detailed article on the legislation -- and the opposition to it by Chief Justice Rehnquist, the American Bar Association and a handful of senators -- reporter Dan Christensen cited a case in which a judge appointed by President Reagan had come under attack by House members for allegedly imposing unlawfully light sentences. TRAC data, however, cited in Christensen's article, showed that the median sentence of the judge in judge in question was on a par with other judges in his district.