The director of the federal Centers for Disease Control and Prevention has spelled out reasons her agency refuses to continue funding a Utah fallout-cancer study. Scientists conducting the research are spelling out why they think she is wrong.

In fact, the surprising end to the study has led its principal investigator, the University of Utah's Dr. Joseph L. Lyon, to speculate about a cover-up.

He wonders if someone decided to kill the project "right now, before we have evidence of additional thyroid problems or other health problems that are related to the above-ground nuclear testing."

On April 5, Dr. Julie Louise Gerberding, director of the Atlanta-based federal organization, wrote to Sen. Orrin Hatch, R-Utah, responding to a query about the CDC's refusal to further fund a study of thyroid abnormalities among former students who were exposed to fallout. Hatch had inquired about the CDC's decision to stop funding the study.

The former students attended Washington County schools in 1965, not long after the end of open-air atomic testing at the Nevada Test Site. An earlier study by Lyon discovered that the group had thyroid tumors at 3.4 times the expected rate. The present research is a follow-up, since thyroid abnormalities caused by radiation can show up years later.

After paying about $8 million, the CDC pulled the plug, saying the study was supposed to be for five years and had been extended twice. Lyon responded that bureaucratic barriers by the CDC had slowed the project. By now, about 1,300 of 4,000 subjects (including a control group) had been examined.

In the letter to Hatch, Gerberding wrote, "The scientific quality of the study was questioned by external scientific reviews conducted by the National Academy of Sciences (NAS) and a special emphasis panel (SEP), a board of scientific experts external to CDC.

"Both reviews focused on the lack of scientifically defensible dosimetry, power and treatment of uncertainty. Those issues form the foundation upon which the study is based."

In 2001, the NAS reviewed the study protocol and determined it was not sufficiently developed or rigorous enough to permit a judgment of whether all its objectives were attainable, she wrote.

"NAS also could not evaluate the scientific merit of the study due to lack of detail regarding the dosimetry methods to be used. The University of Utah responded to NAS' comments but has been unable to reproduce the dosimetry from earlier work," Gerberding wrote.

Her comments dismay U. scientists.

"We were reviewed in 2001 by the NAS," Lyon said. "We responded to that review, even though it doesn't reflect that in this letter."