A new report from a large government study confirms that childhood convulsions are seldom related to the side effects of immunization shots for diseases such as whooping cough.

But, even in the rare instances when they do occur, long-term nervous system damage is unlikely to result, Bethesda scientists say.

Drs. Deborah G. Hirtz and Karin B. Nelson, reporting on the follow-up results of a National Institutes of Health study, sought to reassure parents alarmed by a recent report on WRC-TV, Channel 4, on the risk of permanent brain damage from childhood shots against whooping cough.

They presented data at an American Academy of Neurology meeting here from a follow-up of more than 50,000 children. Of them, more than 2,700 had one or more convulsions by the age of 7.

Of these, 39 children--1.4 percent of those with convulsions--were reported to have had the seizures within two weeks of an immunization. This included 10 cases following shots to protect against DPT (diphtheria, pertussis or whooping cough, and tetanus), 10 following measles vaccinations and the rest involving smallpox, flu, polio, tetanus and unidentified baby shots.

The doctors said that medical examinations up to age 7 showed serious long-term damage in one child, who suffered from a speech disorder but no impairment in intelligence. The child had had lengthy seizures following a third DPT shot at the age of 9 months.

But the other 38 children had no signs of long-term nervous system problems, such as repeating seizures, motor disabilities or mental retardation, said the two National Institute of Neurological and Communicative Disorders and Stroke doctors.

Parents whose children do have seizures should be "reassured," said Nelson, that they are likely to be "normal" in the long run.

The government doctors said that fever, a common side effect of immunizations, appeared to be the culprit in most of the cases. Seizures as a result of fever from all causes occur in 3 to 5 percent of young children.

Hirtz emphasized that the study did not calculate the overall likelihood of a child getting a seizure following an immunization shot.

But she said that the overall health risk from immunizations appeared to be "very, very small" and that the results in the United States are consistent with those of a major Great Britain study. That study found that the risk of long-term nervous system complications following a single DPT shot was 1 in 300,000.

The recent Channel 4 program challenged that number, warning that the risks may be far greater. But medical experts across the country have defended the vaccination effort as necessary to protect against far greater risks of the childhood diseases.