Grafting tissue into the brain or spinal cord in hopes of treating disorders such as Parkinson's disease remains highly experimental despite recent progress, a congressional report said Saturday.

The Office of Technology Assessment concluded more research is needed before it can be known if neural grafting - the transplanting of nerve cells into the brain or spinal cord - helps people stricken by Parkinson's, Alzheimer's, stroke, spinal cord injury or similar neurological disorders.Of the types of tissue being studied for use in neural grafting, tissue taken from the central nervous sytems appears to be most effective, the OTA said. The Reagan and Bush administrations have imposed a moratorium barring the federal funding of any human tests involving tissue taken from aborted fetuses.

Alternatives to fetal tissue might include cultured or genetically engineered cells, or perhaps tissues from other organs or outlying regions of the patient's own nervous sytem, investigators said.

The idea behind neural grafts is that the implanted tissue would either supply nervous system chemicals lost through disease or injury, supply new substance to prolong the survival or prolong the regrowth of nerve cells or directly replace missing nerve cells.

"Even in the case of Parkinson's disease, in which neural grafting has advanced the farthest, additional information needs to be collected before neural grafting can be adapted for general use," the OTA said in the 202-page report.

So far, neural grafts have only been tested in a small number of people suffering from Parkinson's disease, with teams in Sweden and Colorado reporting encouraging early results. Other neural grafting efforts are still at the stage of animal experimentation.