The Air Force, releasing what it called the first statistically valid U.S. study of the effects of Agent Orange, yesterday said fliers who were exposed to the toxic herbicide have not died at greater rates than other servicemen.

The study found no difference in causes or rates of death between a group of 1,247 Air Force personnel actively involved in spraying Agent Orange in Vietnam and a group of Vietnam veterans who were not exposed to the defoliant or were exposed at much lower levels.

"Instead of hearing negative news, we've got the first good news coming out," said Dr. Alvin Young, an Air Force major and medical adviser on Agent Orange to the Veterans Administration. "Despite their exposure, there doesn't seem to be at this point any indication that it's causing mortality."

Scientists who conducted the survey cautioned, however, that its results are preliminary and say nothing about incidence of disease in veterans or of birth defects in their children. More than 16,000 veterans of the war in Vietnam have filed claims--most of which the VA has not accepted--maintaining that their illnesses or their children's conditions stem from exposure to the chemical.

Critics said the veterans examined in the study are so few and so young that only a remarkable increase in cancer rates would show up at this stage.

A panel of the National Academy of Sciences that examined the study design three years ago warned that early results might be "incorrectly interpreted." The academy president cited "the relatively small size of the group to be studied and the relatively short time for which it is proposed to follow the health of the group."

"We're not reporting or claiming anything from this study except that, from what we've seen, there's no unusual mortality," said Maj. Gen. Murphy A. Chesney, deputy Air Force surgeon general. Chesney said the Air Force will report on disease patterns in the study population next fall and will follow the veterans for 20 years.

In particular, the study found only four cancer deaths among the "Ranch Handers" and no deaths attributed to soft-tissue tumors, which have been cited as the likeliest possible ill effect of Agent Orange.

On the other hand, such soft-tissue tumors are considered so rare that their rate among the study population would have had to be five or six times higher than in the normal population to show up definitely in the survey.

The Air Force sprayed Agent Orange in Vietnam between 1965 and 1970 to kill jungle foliage and thus reduce cover for enemy ambushes. The defoliant contained dioxin, the same chemical that recently has caused alarm in communities in Missouri and elsewhere in the United States.

The Ranch Hand personnel handled the Agent Orange, named for the markings on the barrels, wearing no protective clothing.

"The agent at that time was not considered harmful," Chesney said. "They lived in it. They would come home soaking wet from their missions."

However, the Ranch Hands' experience may not be comparable with the exposure of thousands of ground troops, according to an aide to Rep. Thomas A. Daschle (D-S.D.), who has introduced legislation to provide disability benefits to veterans exposed to Agent Orange. The aide, Ryan Krueger, said ground troops could not shower each night, as did the Ranch Hands, and ate and drank food contaminated with the herbicide.