The war of words over possible chemical warfare in Southeast Asia and Afghanistan will probably extensive for quite some time, despite last week's claim by a Harvard professor that so-called "yellow rain" is nothing more than bee feces.

The announcement by Harvard's Matthew S. Meselson, Cabot Professor of Natural Sciences, and Thomas D. Seeley, a Yale biology professor, seems likely only to fuel further the debate over U.S. government charges that the Soviet Union and its allies are waging chemical warfare in Laos, Cambodia, and Afghanistan.

Meselson and Seeley dropped their bee bombshell at a Harvard press conference last week, following a ten-day trip to Thailand in which they observed bee defecation flights and said they were caught in a five-minute shower of bee feces.

The scientists said that these observations confirmed their hypothesis--first advanced at a scientific conference last May--that a natural explanation exists for yellow rain.

But the announcement scarcely was out before the government and other scientists leapt to denounce the findings and stand by their own conclusions that the Soviets are up to mischief.

Imbroglio

One scientist even insinuated that Meselson has a professional are to grind over the yellow rain issue, alleging that Meselson is acting "not as a scientist, but as a politician."

Meselson, an expert on chemical warfare was one of the principal architects of the 1972 Biological Weapons Convention the international agreement outlawing biochemical weapons.

The bitter acrimony over the issue stems from the high political stakes involved.

Some experts feel that if scientists can conclusively prove that the Soviet Union is involved with chemical warfare, it will call into question the reliability of arms control agreements and increase pressure for the United States to develop chemical weapons--long considered unusually cruel.

Neither side on the increasingly polemical yellow rain dispute has been able to produce incontrovertible scientific evidence, and each has relied on what explanation seems most plausible for reports of yellow substances falling from the sky.

The government and its supporters base their conclusions on evidence ranging from persistent refugee reports of chemical warfare and intelligence interceptions of radio communications, to the discovery of a Soviet gas mask in Afghanistan containing illegal trieothecene mycotoxins.

The government also has collected laboratory samples of leaves, rocks, blood and urine from alleged attack sites. These contain what some academic exports say are levels of mycotoxins in excess of what occurs naturally in Asia.

Evidence

"There is a substantial body of evidence collected from other means and methods," said one State Department official, who labeled Meselson's hypothesis "pure speculation."

But following their trip to Thailand, Meselson and Seeley reiterated their previous skepticism over the scientific quality of the State Department's evidence.

This skepticism began with their observations that bee feces bore striking similarities--in size, appearance, and characteristics--to alleged samples of yellow rain, many of which contained pollen.

In various parts of Thailand, the scientists found what they said was the first evidence that Southeast Asian honey bees actually do perform defecation flights, which produce yellow spots similar to what the government has alleged is evidence of yellow rain.

Feces

"People do not recognize these spots for what they are," Meselson said at last week's press conference. "They are in fact the feces of wild honey bees."

Commenting on the State Department's evidence, Meselson said in an interview following the press conference: "They have a lot of evidence, but it is of low quality... They start with a hypothesis, and then they try to collect things that agree with their hypothesis."

Refutation

Referring to samples allegedly containing mycotoxins, he said that scientists have not used proper scientific controls--comparing them with non-contaminated samples--to see if they occur naturally.

Meselson added that because mycotoxins occur naturally in India, he believed they could also appear in Southeast Asia, which has a similar climate.

Meselson expressed similar doubts about the reliability of interviews held with refugees, and he also said that no spent or unspent munition containing toxins has ever been found since reports of yellow rain started seven years ago.

While Meselson has held out for conclusive evidence of chemical warfare, he has drawn criticism from some areas over his conclusions and motives.

Talking Tough

"Continued unsupported speculation on a possible natural explanation of the origin of causalities and deaths from the prohibited use of chemical weapons only serves to divert serious attention from the real issues on chemical warfare," State Department spokesman Alan Romberg told reporters last week.

Another official, who asked not to be identified, called Meselson's allegation that sufficient controls did not been done in the government investigation of samples of leaves, rocks, or blood containing mycotoxins "a bunch of bullshit."

He said that the government "can't manipulate the environment like you can in academic," but had gathered as strong evidence as possible. "We have taken a fairly good number of control samples," he said. "None of these control samples have contained mycotoxins."

Another scientist who has examined samples of yellow rain for the government questioned Meselson's whole approach to the issue.

University of Minnesota plant pathologist Chester J. Mirocha said that Meselson's findings were irrelevant to the whole debate, because the samples of leaves containing mycotoxins did not have the yellow spots which resemble bee feces.

"What I see Matthew Meselson working as is not as a scientist, but as a politician," Mirocha said. He added that in fact Meselson has tried to make facts fit his hypothesis.

Defense

Responding to these changes, Meselson said. "It's a shame to see Mirocha lower himself to ad hominum attacks."

He added that he has published all his work on yellow rain thus far in scientific journals and plans to do the same for his new findings.

"If that's not science, I don't know how to do science," he added.

Meselson repeated his contention that adequate scientific surveys have not yet been carried out to test for mycotoxins.

He added that he and Seeley brought back samples of bee feces and foods to test for such substances--which would be further proof in his mind that they cause the yellow rain.

Part of the problem in getting the State Department to change its position on the subject--even if it is proved wrong--is the heavy stake they have put into their charges against the Soviets.

A change in position could diminish American credibility around the world--a political fact Meselson is well aware of.

"Once the President of the United States and the Secretary of State have said there is chemical warfare, no amount of scientific evidence" can change the U.S. position, he said