A D.C. Superior Court jury yesterday found a 32-year-old Southeast Washington man guilty of first-degree murder in the beating death last February of his girlfriend's 8-year-old daughter.

The jury of seven men and five women deliberated for four hours before finding Rothell A. Perry, of the 800 block of Bellevue Street SE, guilty of kidnaping Yulanda Renee Johnson, beating her with a large rock and then hiding her body in the North Michigan Park Woods near 14th and Emerson Streets NE.

The child was reported missing Feb. 11, 1981, after she failed to return to her home from Keene Elementary School. Two days later, after extensive interrogation by law enforcement officials, Perry led police to the girl's frozen body. A deputy D.C. medical examiner testified that her death was caused by the beating, a knife wound in her throat and exposure.

Perry's lawyer, Irvin Foster, has indicated he intends to argue that Perry was insane at the time of the incident. If the defense decides formally to pursue that argument, a second trial would be required in which the same jury would decide whether Perry was insane. Judge Fred B. Ugast scheduled a hearing for Monday to determine whether another trial is needed.