Sol Z. Rosen, the lawyer for accused murderer Bernard C. Welch, has agreed not to participate in any arrangement to collect his legal fees out of the potential proceeds of a book about Welch's life of crime, according to informed sources.

Welch, on trial for the Dec. 5 murder of cardiologist Michael Halberstam, first disclosed the legal fee arrangement last Sunday in an interview in The Washington Post. Welch said that he would pay his attorney's fees from the proceeds of the book to be written by a New York writer.

But Welch's arrangement, currently under investigation by the D.C. Bar Counsel's office, might violate the Code of Professional Responsibility, the disciplinary rules lawyers must follow here. Those rules prohibit lawyers and clients from entering into such arrangements because it might influence a lawyer's performance during a trial.

Welch appeared in court yesterday as potential jurors were questioned for the second day by Superior Court Chief Judge H. Carl Moultrie I, Rosen and Assistant U.S. Attorney Jay B. Stephens. The prospective jurors were told that Linda Sue Hamilton, Welch's common law wife since 1976, may be called as one of about 30 prosecution witnesses to testify against Welch. No jurors were picked, but a final jury panel is expected to be selected today and the trial formally started.

Rosen has asked Moultrie that he be paid for his representation of Welch with public funds under the Criminal Justict Act. The action will prohibit his receiving any other outside income from his client relating to the case -- including any proceeds from the planned book -- if the plan is approved by the judge.

Rosen's agreement to represent Welch with public funds followed a protest from U.S. Attorney Charles F. C. Ruff's office. Prosecutors voiced the fear that that starting the Welch case before Rosen's fee arrangement was clarifed could endanger the government's entire case because Welch might later be found to have not received a fair trial if Rosen hand an outside financial stake in the trial's outcome.

According to the sources, Rosen and prosecutors met secretly with Moultrie and the defense attorney agreed to take the case as a court-appointed attorney. Rosen, who has declined to comment on the issue, also denied, according to one source, that he had any written agreement with Welch to be paid for the book contract.

Moultrie said that before Rosen could be appointed with public funds, Welch had to file court papers establishing that he is indigent, documents which had originally been requested several months ago.

Welch filed the necessary affidavit on Wednesday, according to an official in the court's Criminal Justice Act office, and a notarized copy was sent to Moultrie. "Once the court has determined that a defendant is eligible" for representation with public funds, according to the official, "it is a violation of the law for (his) attorney to accept funds from that defendant." Moultrie has yet to take final action on the matter.

Moultrie has repeatedly refused to give reporters the affidavit and transcripts of the court session relating to the matter and the principles involved in the issue have declined to comment.

Welch claimed in the interview that proceeds of his book will benefit his three infant children and not himself, since the Internal Revenue Service attached all of Welch's assets and future income. However, Welch apparently also arranged to pay his legal fees through the book proceeds -- assuming the IRS did not also claim the book profits. Rosen would receive up to an agreed-upon five-figure legal fee through potential book profits, according to one source.