OKLAHOMA CITY� State and federal officials are investigating hundreds of cases, including those of 13 people on death row and 10 who have been executed, in which an Oklahoma City police lab scientist may have given improper testimony about evidence.

From 1980 to 1993, police lab scientist Joyce Gilchrist was involved in roughly 3,000 cases, often helping prosecutors win convictions by identifying suspects with hair, blood or carpet fibers taken from crime scenes. But Gilchrist is now the subject of an investigation ordered this week by Gov. Frank Keating to re-examine all of her felony cases after her credibility was denounced by an FBI report that found she had misidentified evidence or given improper testimony in at least five of eight cases the agency reviewed.

The case that helped prompt the investigation involved a man convicted of rape 16 years ago after Gilchrist linked him to the crime through hair evidence. But recent DNA testing determined that semen taken from the crime scene did not match the man, Jeffrey Pierce. And the FBI report contradicted Gilchrist�s findings on the hairs, determining that they did not match Pierce. Officials said Pierce could soon be released.

The immediate focus of the state investigation is the 23 capital trials in which her testimony helped win convictions. Keating�s spokesman, Dan Mahone, indicated the evidence against those defendants was overwhelming, regardless of Gilchrist�s testimony.