The U.S. attorney's office has persuaded the D.C. Bar's disciplinary committee to put off its scheduled hearing tomorrow on charges that Sol Z. Rosen, former lawyer for convicted murderer and master burglar Bernard C. Welch, lied about a book contract and didn't put on an adequate defense.

What troubles U.S. Attorney Stanley S. Harris is that the D.C. Court of Appeals has yet to consider Welch's challenge to his conviction and his 143-year prison term, which could cover some of the same allegations about his lawyer's poor performance that the bar committee is investigating.

Harris doesn't want the bar to uncover anything Welch could use to overturn his conviction. In a letter last month to bar counsel Fred Grabowsky, who oversees complaints about lawyers, Harris said he saw "substantial risks" if both the court and the board were simultaneously reviewing the same facts.

Rosen's attorney, Thomas W. Farquhar, who also had asked for a delay, wants the Court of Appeals to be the first to decide whether Rosen did anything wrong and, if he did, whether it made any difference to the outcome of the case. After all, as Harris points out, the scope of review of a lawyer's conduct would be far narrower in the appeals court than in the bar committee. And if the appeals court clears Rosen, it would be a mighty important character reference to take to the bar committee.

That's fine for Rosen, but it leaves Welch's new lawyer, Alan Soschin, out in the cold. Soschin agrees that the bar hearing might well raise some important points that Welch may use to overturn his conviction. That's precisely why he wants the bar hearings to proceed as scheduled.

But the bar board, although an independent investigative body, has bowed to the prosecutor's plea that the "public interest" demands that the U.S. attorney concentrate on making sure that Welch's conviction sticks and worry later about Rosen. A bar counsel spokesman says they are delaying the hearings as a matter of "courtesy" to the prosecutor's office.