A judge must make absolutely sure that a defendant understands every detail of a plea-bargaining arrangement before accepting a guilty plea in a criminal case the U.S. Court of Appeals ruled here yesterday.

The appeals court made its finding, an apparent expansion of rules governing plea-bargaining agreements in U.S. courts, in a case in which an alleged drug figure pleaded guilty and then attempted to withdraw his plea before sentencing.

The judge refused and sentenced the defendant to a four to 15-year prison term. But the appeals court said he must now allow the guilty plea to be withdrawn and let the defendant go to trial.

At issue in the case was the prosecutor's desire to state the government's position on the sentencing of Winfield Roberts. The prosecutor said at the time of the plea that he would make such an statement on te sentencing date.

The prosecutor, Assistant U.S. Attorney Joseph McSorley of the major crimes division, then filed a lengthy and strongly worded memorandum describing Roberts as a major heroin dealer and asking for a substantial prison term.

Roberts and his attorney then attempted to withdraw the guilty plea, saying the prosecutor had never said he would ask for substantial time but merely that he reserved the right to ask for some sort of prison term. Roberts would not have pleaded if he had known about the request for substantial prison time, his attorney added.

The defense disputes McSorely's contention that he had specially reserved the right to ask for substantial time.

At the time he took plea, U.S. District Judge John H. Pratt should have delved more deeply into every aspect of the plea-bargaining arrangement instead of asking only the minimum questions required when a guilty plea is taken in federal court the appeals panel found.

In addition, the attorneys for both sides should have made sure that every detail was brought before the judge.

"The parties are required to inform the trial judge of all the promises that have been made, not only those which they happen to consider important," U.S. Circuit Judge George MacKinnon wrote in the appellate opinion. Agreeing with MacKinnon were U.S. Circuit Judges J. Skelly Wright and Spottswood Robinson II.

"We do not suggest that there was any conscious effort at concealment by any of the parties; the mere fact that there was not a full disclosure of the plea agreement is sufficient basis" for allowing the plea to be withdrawn, the court added.

The ruling by the appellate court has the effect of reinstating a five count drug distribution conspiracy case against Roberts, instead of the one count of conspiracy to which he first pleaded guilty.

The court made it clear that if Roberts goes to trial and ultimately is convicted of all five counts, "there is nothing to prevent the court from imposing some other sentence more severe" than the 4- to 15-year term that previously was imposed.