The D.C. Court of Appeals, citing "gross incompetence" by a defense lawyer, yesterday reversed the murder conviction of a Southeast Washington man who has spent more than six years in prison for the 1975 stabbing death of a neighbor.

Associate Judge William C. Pryor, writing for a unanimous three-judge panel, said Nathaniel Harris, 26, was denied his constitutional right to the "effective assistance" of a lawyer during his 1976 trial for the murder of Furman Turner. A jury found Harris guilty of second-degree murder, and Superior Court Judge Tim Murphy sentenced Harris to serve 15 years to life in prison.

Pryor said that Harris' lawyer, Edward Kehoe, "did not investigate the case, nor minimally consult with his client, nor make even rudimentary preparation for trial." Kehoe's "conduct blotted out the essence" of Harris' ability to argue that he stabbed Turner in self-defense, Pryor said.

According to the opinion, Harris was chased into his backyard by Turner, who was armed with a poker. After he had been hit several times, Harris reached for a garden tool and stabbed Turner, according to the opinion.

Pryor said that Kehoe never visited the scene of the crime nor attempted to locate any of the potential witnesses, including one neighbor who said she saw Harris calling to his mother to open the back door and attempting to get inside before he turned to confront Turner.

"In my view, my representation was adequate," Kehoe said in an interview yesterday. The problem, he said, was that while Turner was stabbed 16 times, Harris would never admit that he had any weapon in his hands, which "destroyed" the credibility of his testimony.

Harris' present lawyer, Kenneth E. Labowitz, said yesterday that Harris, now in a federal prison in Alabama, would be brought back to Washington for a hearing before Murphy. Murphy may decide to order a new trial, Labowitz said, or it is possible that the U.S. attorney's office may reduce the charges or dismiss the case altogether.