A D.C. Superior Court jury yesterday convicted Jessie James Clark of first-degree murder in the shooting death of a Southeast Washington liquor store manager.

The jury, which deliberated 2 1/2 hours, found Clark, 31, guilty of the slaying of Alan Rosenblatt on Feb. 8, 1980, during a holdup attempt at Albert's Liquor Store, 328 Kentucky Ave. SE. Clark also was convicted of armed robbery, assault with a deadly weapon and carrying a pistol without a license. The murder conviction carries a mandatory prison sentence of 20 years to life. Judge George H. Revercomb set sentencing in the case for Aug. 3. t

During the six-day trial, defense attorney James E. Joyner argued that Clark should be found not guilty by reason of insanity on the basis of medical records and testimony by psychiatric experts.

Assistant U.S. Attorney Jay B. Stephens called expert government witnesses in efforts to establish that the crime was "well planned and organized" and "not a bizarre crime of any kind."

Clark, who is currently serving a jail term on a previous conviction, sat expressionless as the jury foreman read the verdict.

Clark was arrested shortly after he stumbled from Albert's Liquor Store with gunshot wounds in his chest in the wake of a shootout with Rosenblatt. Store owner Leon Friedman, who saw the injured Clark get into his car, gave chase and called the police from a phone in his car.