U.S. Attorney Jay B. Stephens urged a federal judge yesterday not to split the case against D.C. Mayor Marion Barry into two trials, saying in court papers that a second trial would be wasteful and could "exacerbate potential problems of prejudice."

Barry's lawyers had asked U.S. District Judge Thomas Penfield Jackson to sever the six new charges contained in an indictment returned against Barry two weeks ago.

Barry's lawyers said they lacked time to prepare a defense for the new charges before the scheduled June 4 trial on the first indictment.

In his response filed last night, Stephens vigorously disputed that claim, telling Jackson that the defense "has had ample time to prepare for trial on the additional charges . . . .

"Moreover, {Barry} has substantial personal knowledge of the charges since they are based on his own actions possessing and using cocaine and crack."

In addition, Stephens argued that it would be improper to separate the newer charges because that would "require presentation of the same evidence and testimony of the same witnesses" as would the original charges.

Barry's lawyers are expected to dispute that assertion today in a hearing scheduled by Jackson on the pretrial motions.

Legal experts have said Barry's lawyer, R. Kenneth Mundy, asked for the separation of charges at least in part to keep out testimony from longtime Barry friends about cocaine use in a first trial that would include three felony charges against the mayor.

Barry is facing a 14-count indictment that alleges he lied to a federal grand jury, possessed cocaine and conspired to possess cocaine between 1984 and Jan. 18, when he was arrested at the Vista Hotel.

The three perjury charges, which are felonies, were contained in the first indictment that was returned in February. That indictment also charged Barry with five counts of possession of cocaine. The second indictment added five possession counts and the conspiracy charge, all of which are misdemeanors.

Stephens also said he would disclose the names of unindicted co-conspirators in the case only if a federal judge orders that Barry and his lawyers keep the names secret until the trial.

In various pretrial motions, Mundy has asked Jackson to dismiss all charges, suppress the videotape of Barry's arrest at the Vista, suppress other evidence and try the Vista cocaine possession charge separately.

In support of their request for names of co-conspirators, Barry's lawyers have alleged that Stephens has kept the names secret to foil their trial preparation efforts, and they have said it is virtually impossible to get ready for the trial without the information.

"We have to know what team we're playing against or we can't have a fair game," Mundy said after Barry pleaded not guilty to the new charges last week.

Mundy also has asked Jackson to order Stephens to provide copies of grand jury testimony and other statements made by government witnesses before the trial begins. Mundy said he needs the material to prepare Barry's defense.

Responding to that request, Stephens said in court papers filed yesterday that he had agreed to provide Barry's lawyers with the material, but he used the occasion to take a legal jab at the defense.

"Once again, {the defense} seeks to blame the government . . . . If the defendant planned to wait to investigate until he received the material that he is not entitled to receive until the trial begins, he has only himself to blame for not being prepared," Stephens said.