After deliberating for six hours yesterday a Prince George's County jury found Robert Willie Young guilty of murdering Greta Kerry Sorrell, an alleged heroin courier, in a Capitol Heights apartment in January 1978.

The jury also convicted Young of assault with intent to murder in the wounding of Sorrell's husband, Joseph, in the same incident.

Young is alleged to be part of a heroin smuggling operation that brought at least $30 million of heroin from Europe to the Washington area. Security for the 10-day trial was the tightest in Prince George's county in more than a decade, sheriff's department officials said.

During the trial, assistant state's attorney Thomas Blair argued that Young recruited the Sorrells in July 1977 to smuggle heroin from Amsterdam to the United States.

When a dispute arose about whether the Sorrells should be paid for a trip in which they failed to bring back any drugs, Blair said, Young shot the Sorrells. Young flatly denied the sworn testimony of Joseph Sorrel that he had done the shooting.

Blair said that he will ask for maximum sentence of life imprisonment for the murder charge when Young is sentenced on Sept. 17. Defense attorneys said Young plans to appeal the verdict.