An assistant U.S. attorney here circulated a memorandum among fellow prosecutors last fall in which he accused the judge in a rape case of "conspiring . . . to rob him of his credibility with the jury," and labeled the defendant's attorney "the most treacherous, unscrupulous advocate I've ever seen."

The memo, introduced at a hearing yesterday by the public defense counsel in the case, set off a courthouse tempest that threatened to upset the delicately balanced adversary relationship between the U.S. Attorney's office and the Public Defender Service.

D.C. Superior Court Judge George H. Revercomb, who is presiding in the case, was visibly upset over the memo and admonished its author, assistant U.S. attorney Cary M. Feldman. Revercomb called the memo "an utterly sad display of a lawyer's view of the judge's role in a trial, the saddest display I have seen in my 12 1/2 years on the bench . . . "

Public defender James McComas, who offered the document as evidence that Feldman had waged a vindictive campaign to convict a man charged with raping a 12-year-old girl, refused to say how he obtained the memo, which was distributed among felony prosecutors in Superior Court last October.

The case has provoked unusually acrimonious confrontations between McComas and prosecutors, and last month Revercomb ordered a new trial for defendant Ondrea Lamont Gant on grounds that Feldman had improperly influenced the jury by eliciting testimony that Gant had once been convicted on a robbery charge. Revercomb said at the time that Feldman's conduct was "even worse" than that of prosecutors in similar cases in which convictions have been overturned.

At one point in yesterday's hearing on McComas' motion to dismiss the charges against Gant entirely, Revercomb declared that Feldman "was emotionally involved" in the case "and was seeking a conviction no matter how he could get it because of that emotional involvement."

Late yesterday, U.S. Attorney Stanley S. Harris issued a brief statement calling Revercomb "a very experienced, able, and honorable trial judge.

"It is extremely regrettable," Harris said in the statement, "that defense counsel not only somehow has obtained a confidential internal memorandum which was written by an assistant United States attorney immediately after a vigorously contested trial, but . . . inexplicably has chosen to make that memorandum public."

Public Defender Service Director Frank Carter was unavailable for comment.

Feldman wrote the two-page memo shortly after Gant, 26, was convicted of rape, carnal knowledge and enticing a minor child for the purpose of taking indecent liberties.

In the memo, he attacked McComas for offering 10 motions for a mistrial, but, Feldman wrote, he was "more outraged at the judge Revercomb ," who, he complained, "sided with McComas and the child molester, instead of the victim and me, throughout the trial."

Feldman wrote that Revercomb's instructions to the jury "constituted the most one-sided charge . . . I have ever seen." He added: "I will never forgive Revercomb for conspiring for six days with McComas, without provocation, to rob me of my credibility with the jury."

Gant was convicted and, "In the end," Feldman wrote, "beating this defendant, this attorney and this judge was sweet vindication."

Court sources said that a report on Feldman's conduct in the case would be sent to the Justice Department for a routine review. The sources said also that prosecutors are considering requesting that the Public Defender Service implement a policy that would prohibit its lawyers from making such government memoranda public.

Prosecutors and public defenders work closely together under generally amicable terms at Superior Court, meeting regularly in the U.S. attorney's offices to discuss evidence and possible plea bargains and to exchange materials in hundreds of cases each year.

Prosecutors said yesterday they were disturbed that Feldman's memo got out of the offices, and that the unprecedented introduction of such a document in court might force restrictions on how they will conduct business with public defenders in the future.

McComas' motion for dismissal of the charges cited a Washington Post article quoting "veteran lawyers" as saying that Revercomb's overturning of the Gant conviction went "far beyond previous court decisions on what prosecutors can tell a jury about a defendant's record."

McComas maintained in court papers that prosecutors were the sources behind the story, and that they violated court rules by commenting on the case anonymously. He also cited efforts by prosecutors to have Gant detained pending trial, Feldman's alleged misconduct at the trial last fall and the memorandum as evidence that prosecutors had improper motives in the case.

Revercomb denied the motion for dismissal and set a new trial date for Gant in July.