The agency that disciplines D.C. lawyers accused attorney Sol Z. Rosen yesterday of lying to a Superior Court judge last March about the existence of a book contract under which he could have received up to $50,000 in legal fees for representing Bernard C. Welch, the convicted slayer of cardiologist Michael Halberstam.

If upheld, the accusations could lead to overturning Welch's murder conviction, according to Welch's new lawyer, as well as to disciplinary action against Rosen.

The Office of Bar Counsel, which investigates alleged lawyer misconduct in the District, accused Rosen of violating nine provisions of the lawyers' Code of Professional Responsibility.

The report alleged that Rosen engaged in conduct "involving dishonesty and misrepresentation" in his defense of Welch, failed to adequately prepare Welch's defense, and violated the confidentiality of his relationship with Welch by publicly claiming, prior to Welch's sentencing, that his client was guilty.

"He Rosen engaged in conduct that was prejudicial to the administration of justice . . . ," the report said. "While representing his client, Rosen failed to conduct any meaningful independent investigation on behalf of his client, failed to meaningfully communicate or discuss the case with his client, and he failed to adequately prepare the case for trial."

The charges, which were filed by Assistant D.C. Bar Counsel Wallace E. Shipp Jr., are not allegations of criminal misconduct but rather purported violations of the District's rules for ethical conduct by lawyers. If they are upheld by the Board of Professional Responsibility and the D.C. Court of Appeals, Rosen could face disciplinary action ranging from a reprimand to suspension or disbarment.

"When you sleep with dogs, you wake up with fleas," Rosen said yesterday, strongly denying the Bar Counsel's allegations. "I did everything I could to defend the case. Welch tried to set me up. I have no contract with anyone. I have never had one. I saw him about 12 times in jail. I talked to police, talked to prosecutors, reviewed the evidence. Simply, the government's case was overwhelming against him."

Attorney Alan B. Soschin, who is handling Welch's appeal, said if the charges that Rosen failed to adequately represent Welch are accurate, it might "necessitate a reversal" of Welch's convictions. United States Attorney Charles F.C. Ruff, whose office prosecuted Welch, declined to comment because of the pending appeal.

Welch first disclosed the book contract in an interview with The Washington Post shortly before his trial last April. But he and Rosen both denied in court before Chief Judge H. Carl Moultrie I that they had a book contract. On April 10, Welch was convicted by a jury of murder, burglary and other charges, and Moultrie later sentenced him to a minimum of 143 years in prison.

The report alleges, however, that prior to the trial, Rosen "knowingly acquired or sought to acquire a proprietary interest in any literary right arising from his client's case. He sought and/or allowed himself to have a beneficial interest in a trust agreement dated February 20, 1981, for a fee not to exceed $50,000."

In denying the existence of the contract to Moultrie, the report alleged that Rosen made a "false statement of fact."

Such literary arrangements are prohibited because of the potential for a conflict of interest that could color a defense attorney's courtroom conduct.