Sol. Z. Rosen, attorney for convicted killer Bernard C. Welch, yesterday sharply attacked Welch's formal complaint that the lawyer had not represented him properly and said Welch "was guilty, he knows it, he got convicted, and he doesn't want to face the music."

Rosen, whom Welch has charged with ineffective legal assistance in his trial for the murder of Washington cardiologist Michael Halberstam, said Welch's allegations are "the last gasp of a dying man. . . He hopes to embarrass me. He's a mean, vicious guy. He'll stop at nothing to achieve his ends and just doesn't care who he hurts."

Rosen's comments were in response to a 12-page handwritten complaint by Welch to the D.C. Bar Counsel. It followed a preliminary statement Welch filed earlier last week in which he claimed Rosen failed to prepare his defense adequately and had spent most of his time promoting Welch's literary interests. The Bar Counsel is investigating the allegations against Rosen.

In his latest complaint against Rosen, which was filed last Friday and released by the Bar Counsel's office yesterday after Rosen waived confidentiality, Welch alleged that Rosen was "furious" that Welch had discolsed in a Washington Post interview an arrangement by which Welch would pay Rosen legal fees from the proceeds of a book about Welch's life.

Rosen denied knowing about such an arrangement in pretrial questioning by Chief Judge H. Carl Moultrie I.

Welch also complained about statements Rosen made to reporters before and after his trial, including an interview with Washingtonian magazine, in which Rosen was quoted contemplating a possible movie about Welch. Welch claimed Rosen said the Washintonian article would "increase the value of th book or make the public more interested in it." A New York writer is writing the story of Welch's life.

"The charges are all spurious," Rosen said in an interview yesterday."Everything was okay during the trial and all this is after the fact." Rosen must file a formal response with the D.C. Bar Counsel's office, which then will determine if the case should be referred for disciplinary action.

Welch was convicted on April 10 of fatally shooting Halberstam at his Northwest Washington home last December 5. He also was convicted of 10 other charges, and is scheduled to be sentenced on May 22.