The Supreme Court awkwardly but unanimously ruled itself and other all federal judges a pay raise yesterday.

The justices also conceded that the action was a conflict of interest but said they had little choice in the matter because no one else could act this, they said, is the "ancient Rule of Necessity," which "still retains its vitality" after 500 years.

The case arose after lower federal court judges challenged congressional actions from 1976 to 1979 blocking cost-of-living pay raises for all high-level federal employes, including judges. The judicial pay cuts in two of those years were unconstitutional, the court ruled yesterday.

The Constitution bars reductions in a judge's pay while in office as a way of maintaining the judiciary's independence. In 1976 and 1979, the court said, Congress acted unconstitutionally in blocking the raises because they were already in effect in those two years. In the other two years, Congress acted before the effective date, making those actions constitutional, Chief Justice Warren E. Burger wrote for the court.

Burger will receive $84,700 annually instead of $75,000 as a result of the decision. The other high court justices will get $81,300, up from $72,000. Federal District Court judges' pay will increase from $54,500 to $61,600.

Though yesterday's result was not a surprise, there were two signs of unusual awkwardness at the court. Though the printed opinion said the ruling was "unanimous" and made no mention of any justice not participating, the press office later said that Justice Harry A. Blackmum had not taken part in the decision. Neither the press office nor Blackmum would provide an explanation.

In addition, court opinions are not supposed to be discussed with anyone outside the high court until they are announced from the bench. Burger has been adamant about this, saying that a justice could change his mind at the last minute and thus any advance leak of a decision could be in error, or, if accurate, could affect millions of dollars of Wall Street investments.

Yesterday, however, press officer Barrett McGurn said he discussed the opinion with officials at the Administrative Office of the Courts an hour and a half before it was announced in order to prepare a fact sheet on the opinion's impact. The sheet was given to reporters later.

In addition, the adjectives used to describe the Rule of Necessity reflected a concern for public, as well as legal, perceptions. It was variously called "ancient," time-honored," "consistently applied" and "well-settled."

It applies, Burger wrote, because it would impossible to convene a panel of federal judges that had no conflict of interest, although there was no indication of whether the chief justice had tried to convene such a panel. If the justices declined to rule, he said, "the public might be denied resolution of this crucial matter. . . . On balance, the public interest would not be served by requiring disqualification."

The Constitution's Compensation Clause, on which the court based its ruling, is designed to maintain "a judiciary free from control" and judges "free from potential domination" by other branches of government, Burger wrote.

Besides, he added, the Compensation clause serves another, related purpose. As well as promoting judicial independence, it ensures a prospective judge that, in abaondoning private practice -- frequently more lucrative than the bench -- the compensation of the new post will not diminish. l

"Beyond doubt, such assurance has served to attract able lawyers to the bench and thereby enhances the quality of justice," he said.