An attorney for Bernard C. Welch asked the D.C. Court of Appeals yesterday to overturn Welch's conviction for the murder of Washington cardiologist Michael Halberstam, arguing that a lower court improperly allowed some evidence to be introduced at trial and that Welch was denied an effective defense.

But government prosecutors, arguing against Welch's motion for a new trial, contended that proper procedures had been followed and that his conviction was based on "overwhelming evidence." Chief Judge Theodore R. Newman Jr. said he understood the government's position to be that "Houdini couldn't have won this case for the defense."

Welch was sentenced to life after his conviction two years ago in the Dec. 5, 1980, slaying of Halberstam, who was shot when he interrupted a burglary of his Northwest Washington home but ran down his assailant with his car before succumbing to mortal wounds.

Welch's attorney, Alan B. Soschin, told a three-judge appellate panel that the conviction should be overturned because Welch was denied a request for an additional defense attorney at trial and because police improperly seized evidence from his car and his Great Falls home.

Soschin also argued that Welch was denied participation in the selection of the jury that convicted him on counts of murder, burglary and grand larceny, and that a conflict existed between Welch and his trial attorney, Sol Z. Rosen, over a trust Welch said he established to pay for his court-appointed defense.

Judge Newman described the case as "a routine, garden variety felony murder and burglary in the District."

Newman said Welch "sat on his rights" when he failed to ask to be present during pretrial jury questioning, and described the alleged conflict with his attorney as "self-inflicted."

According to Soschin, police illegally seized evidence from Welch's car and his Great Falls home. Both the car and the house were registered in the name of Welch's common-law wife, Linda Sue Hamilton, who gave police written consent to make the searches.

Soschin contended that her consent was improperly obtained because she was "shaken and upset" when she gave it, and that she was not authorized to allow a search of Welch's personal items.

Soschin also argued that D.C. Superior Court Chief Judge H. Carl Moultrie I, who presided over the trial, should have allowed Welch to be present during questioning of prospective jurors in the case.

Assistant U.S. Attorney Wendy Bebie responded that consent for the searches was properly obtained and that Welch never asked to be present during jury selection. Bebie said Welch "was like a kid in a candy store" when he asked Moultrie for a second defense attorney.

The court will act on Welch's request for a new trial at a later date.