D.C. Superior Court officials have decided to delay implementing guidelines that would reduce disparities in felony sentences in light of the current city prison overcrowding crisis and changes in parole practices.

Chief Judge Fred B. Ugast said in an interview last week that the 19-member Sentencing Guidelines Commission had decided to reconsider the proposed guidelines and examine whether any modifications should be made to the numerical ranking system that would require judges to hand down sentences within narrow ranges.

The proposed scoring system, described in a draft report issued in February, would eliminate much of the discretion judges now have in sentencing and could result in slightly longer prison terms for offenders sent to city facilities.

City officials are currently scrambling to meet court-ordered population limits at the D.C. Jail and Lorton, which already house about 50 percent more than their rated capacities. In addition, prison officials said the prison population has been growing by about 200 prisoners a month in the past six months, primarily because of the District police department's massive crackdown on drug use.

Such an "exacerbated prison situation," Ugast said, was taken into account by commission members when they decided to delay implementing the guidelines originally scheduled for a test this fall. Another concern of commission members, Ugast said, was whether the 1984 data upon which they based their recommended sentencing ranges might now be "obsolete" because several important factors had changed since then. Those factors include the explosion of drug arrests and the recently enacted "good time" credit measure that can reduce an offender's minimum prison term by up to a third.

The projection of a two-month increase in the average prison term spurred six commission members, including D.C. Council Chairman David A. Clarke, a Democrat and the mayor's representative, to issue a minority report calling for reduction of the recommended minimums.

Ugast said in the interview that while some commission members wanted to reduce the recommended minimums to reflect the projected increase in prison stays, others wanted to increase them because of the reduction incurred with the good time credit bill.

As a result, he said, most commission members felt that a new study of sentencing practices is needed. The survey, he said, will begin in September and includes all felony sentences meted out by Superior Court judges for at least 90 days and up to 120. The survey could delay implementation of the guidelines on a pilot basis for up to nine months.

Ugast cautioned, however, that although commission members were sensitive to the prison overcrowding situation, the new study might not result in a reduction of the recommended minimum.

Under the proposed guidelines, judges would score a defendant's past and present offenses, and in some cases injury to the victim, to arrive at a narrow sentencing range. For example, a person convicted of rape today could receive a sentence from probation to 15 years in prison.

Under the recommended guidelines, a person with no previous convictions would be ordered to spend about four years in prison, while a defendant with two previous convictions for serious offenses would be sentenced to a minimum of about 5 1/2 years in prison.