University of Maryland researchers have detected high levels of a thyroid hormone in the victims of "crib death." The finding eventually may help identify babies whose lives are at greatest risk.

Experts consider the discovery, reported in the Journal of Pediatrics, to be the first identification of a specific chemical abnormality in those who die of the mysterious sudden infant death syndrome (SIDS).

"It opens up a totally new vista of research," providing the first clue that hormones crucial to regulating a variety of body functions may play a role in the deaths, said Dr. J. Tyson Tildon, who supervised the research. "Whether it is the cause of death or a consequence of another factor remains to be determined."

If more research confirms the finding, Tildon said he believes it could lead to a simple blood test to identify infants at risk. But he cautioned that that prospect is at least "two or three years" away.

Tildon, who heads the research unit at the university's SIDS Institute in Baltimore, said the finding was unexpected and likely to be controversial among scientists searching for the cause of the condition. SIDS kills about 8,000 babies in this country each year and accounts for as much as 50 percent of all infant deaths.

The study, by graduate student Marco A. Chacon, involved measurements of a thyroid hormone called "tri-iodothyronine," or T3, in 50 babies who had died of SIDS at about 15 weeks of age.

They were compared with two control groups consisting of 18 infants who had died of other causes and 12 healthy babies. Additional hormone samples were taken from adults who had died unexpectedly as well as healthy volunteers.

The Maryland researchers found that the T3 levels in 88 percent of the SIDS group were three times the average in the control groups.

Tildon said that the higher T3 levels might help explain many earlier findings in SIDS victims, including alterations in the central nervous system, the presence of excessive "brown" fat around the adrenal gland and fever at the time of death. It also may explain the irregular heartbeat found in so-called near-miss SIDS babies.

SIDS babies also have been found to have retarded growth, and experimental animal studies with the thyroid hormone have shown similar effect, said Tildon.

However, he said, the elevated T3 appears to fall contrary to a widely held theory that SIDS babies have chronic hypoxia, or low oxygen consumption, related to interrupted breathing during sleep. Previous experiments would have suggested that the T3 levels would be significantly lower rather than higher, Tildon said.

He and others emphasized that it was too early to tell how the elevated hormone pertained to the cause of SIDS. Tilden said that it might suggest a different mechanism or that there may be a missing link that ties in with the theory of interrupted breathing during sleep.

Dr. Marie Valdes-Dapena, a researcher at Philadelphia's St. Christopher's Hospital for Children who has studied SIDS for more than 20 years, said that the T3 finding could be important and "may lead us places we've never been before." But she cautioned that confirmation was needed, particularly since several leads in the past had not panned out.

Dr. Herbert Samuels, an endocrinologist at New York University Medical Center, called the study "very interesting" and said that the elevated thyroid hormone could well cause changes leading to sudden death in infants.

Dr. Alfred Steinschneider, director of the SIDS Institute, called it an "important advance" that would be followed up with testing of hormone levels in babies thought to be at risk under very broad criteria.