In a decision that could affect thousands of former soldiers, the Board of Veterans Appeals has decided to award service-connected disability benefits to a retired Army veteran who claimed the leukemia he suffers from resulted from exposure to radiation during a 1957 nuclear weapons test.

Donald C. Coe, of Tompkinsville, Ky., whose case was ruled on Tuesday, was one of 300,000 servicemen who took part in nuclear weapons tests at Nevada or Pacific sites between 1948 and 1958.

Some 40,000 of the soldiers, including Coe, participated in the 1950s in a series of nuclear tests in which troops conducted maneuvers through the test site within hours of the explosion. The other soldiers were witnesses to nuclear explosions.

About 2,400 former soldiers who participated in the tests recently reported to the Defense Department that they have subsequently come down either with leukemia or some other form of cancer.

Coe's case was the first time the board found "it is reasonably probable" that the radiation exposure during the 1957 weapons test called "Smoky" was a "competent causative factor" in leukemia that appeared 20 years after exposure and 13 years after Coe's retirement from service.

A VA regional board will now determine the extent of Coe's disability because of the leukemia and set the amount of compensation and benefits due him.

Since he has been in and out of the hospital during the past year, and had his spleen removed last February, it was likely he will be considered 100 percent disabled. In that instance, according to congressional sources, the [WORD ILLEGIBLE]-year-old Coe would be eligible to [WORD ILLEGIBLE] a month plus allowances for his seven children.

In addition, his wife and children would be eligible for educational benefits under the GI Bill.

Current, Coe gets a $165-a-month pension.

Contacted by phone yesterday, Coe said he was "happy they seen it my way; I couldn't see them finding it any other way than I was affected by the radiation."

Last January, Coe's physician in Nashville said said the Smoky test veteran was too ill to go to Washington to testify at congressional hearings on the Nevada nuclear tests.

Yesterday, Coe said, "I'm holding my own." He said he goes to the hospital once a month to get his blood checked and take medicine to build up his white cell level.

The cases of Coe and Paul C. Cooper, another ex-GI at the Smoky test, created the first public interest in whether there was a connection between low-level radiation exposure of GI nuclear test participants and subsequent development of leukemia and other forms of cancer.

Cooper, who died of leukemia last February, was the first publicized case. The VA, on appeal, awarded him full disability last year but tied the finding not to radiation but to symptoms that appeared while he was still in service.

Coe's case was taken up by his congressman, Tim Lee Carter (R-Ky), a medical doctor and ranking Republican on the House health and environment subcommittee.

With Carter and subcommittee Chairman Paul Rogers (D-Fla.) leading the way, an investigation was opened into the use of GIs during the 1950s nuclear weapons tests.

An initial inquiry into the Coe and Cooper cases by a doctor at the Atlanta-based U.S. Center for Disease Control was expanded and soon found six additional leukemia cases among the 2,235 soldiers who were in maneuvers after Smoky, a 45-kiloton shot, was detonated. The weapon was three times more powerful than the atomic bomb dropped on Hiroshima in 1945.

Although several physicians termed the initial Smoky leukemia findings - more than twice as many cases as expected - statistically significant enough to suggest there may have been a relationship between the radiation and the illness, most government doctors maintained to the Rogers subcommittee that such a connection did not exist.

The question of long-term health effects of low-level radiation - such as that at Smoky - has recently grown into a controversial issue in the medical and atomic energy communities.

The VA's record in awarding service-connected benefits to the few veterans who claimed their diseases stemmed from low-level radiation is inconsistent.

Over the past 10 years, at least 10 such awards were made to veterans but many more were turned down - mainly because the veterans could not prove he was at the test he claimed or that the radiation dose received was considered, too low. In the previously approved cases, however, the veterans showed that during their active service there were symptoms of the disease that later appeared.

In Coe's case, no such finding was made. His symptoms first occurred in late 1976, years after retirement.

The recent Rogers hearings proved many military records of test participants were inadequate or previously unavailable. As a result, some veterans who had been turned down reapplied for VA benefits. others who never filed claims began to do so.

A VA official said yesterday he had no numbers available but said "there was a lot of increased activity" in the filing of radiation-related claims.

It was against that background that the Coe case was decided.

According to the VA board record, material filed last month by Carter included a letter from the director of industrial safety and applied health physics at "a prominent nuclear laboratory," whose name was withheld.

This individual, who participated in Smoky, said the fallout from that test "was the greatest of any he had witnessed at the test site."

Yesterday, Carter said he was "deeply gratified" by the Coe decision and said it "will mean a great deal to thousands of others."

It was Carter who informed Coe's wife by phone yesterday morning of the VA award.

On Wednesday, Coe had asked his wife to call a VA official in Washington to see if any conclusion had been reached in the year-old case. The official, who knew it had been decided favorably for the veteran, said she would be hearing by mail.

Contacted yesterday, the official said, "I didn't tell her because until a decision gets out in the mail it isn't promulgated. I told her she could wait one or two more days."