Lawrence W. Smart, 30, was found guilty yesterday of first-degree murder for strangling his girlfriend more than three years ago in Prince George's County. Smart contended initially that someone else had killed Kathleen T. Campbell, 38, in December 1979, but confessed his guilt Wednesday while he was testifying in county circuit court.

Prosecutor Robert Harvey told jurors that Smart strangled Campbell w0053 ----- r d BC-04/29/83-REGION05 04-29 0001 Man Guilty in P.G. Slaying

Lawrence W. Smart, 30, was found guilty yesterday of first-degree murder for strangling his girlfriend more than three years ago in Prince George's County. Smart contended initially that someone else had killed Kathleen T. Campbell, 38, in December 1979, but confessed his guilt Wednesday while he was testifying in county circuit court.

Prosecutor Robert Harvey told jurors that Smart strangled Campbell in her apartment in the county, then threw her body from a bridge over the Shenandoah River near Front Royal, Va. The body were found seven months later, 14 miles downstream in West Virginia.

Smart was arrested last October--more than two years after an arrest warrant had been issued--when Metro transit police said they saw him kicking a farecard machine.