Dr. Matthew S. Meselson, Cabot Professor of the Natural Sciences, is no stranger to controversy.

Researching recombinant DNA in the mid-'70s, he was embroiled in the then-contentious debate over what safeguards were needed to oversee the potentially hazardous materials. In 1970, Meselson went to Vietnam in the midst of war to monitor the usage of Agent Orange. In recent years, he has been an advocate of greater government attention to Vietnam veterans exposed to the defoliant. This spring, the biochemist's name appeared on an Environmental Protection Agency (EPA) hit list of some 90 scientists singled out for exclusion from EPA advisory boards because of their liberal political views.

But above all, Meselson--who won fame for demonstrating how DNA duplicates itself in dividing cells--has been associated with strong opposition to chemical and biological warfare. He was, as a government adviser, one of the moving forces behind the 1972 international treaty that banned the development of biochemical weapons. Now, Meselson is garnering headlines as the principal challenger to the U.S. Government's position that the Soviet Union or its allies are using deadly chemical weapons in Southeast Asia and Afghanistan.

Meselson has long said that the evidence is suspect that the Soviets are spraying "yellow rain"--particularly the prohibited chemical trichothecene mycotoxin. And now, he has an alternative theory to what's going on. At the end of May, at the annual meeting of the American Association for the Advancement of Science in Detroit, he and a few other scientists dropped the widely publicized' "be" bombshell. Essentially, Meselson and his colleagues are arguing that the spots on leaves and rocks cited by the government as evidence of yellow rain may well be nothing more than bee excrement. Samples of bee feces collected at Harvard bore striking similarities--in size, general appearance, and specific characteristics--to samples and descriptions of samples of spots said to be yellow rain, according to Meselson and four other scientists--including. Harvard botanist Peter S. Ashton, director of the Arnold Arboretum.

Meselson and these scientists acknowledge that the bee theory does not fully explain all parts of the chemical warfare riddle, among them persistent refugee reports of yellow rain, and illness and death associated with yellow rain: the discovery of trichothecene mycotoxins in alleged samples of yellow rain, as well as blood and urine, and a Soviet gas mask found in Afghanistan containing the illegal toxin. Nevertheless, Meselson sums up, "Whatever the source of these toxins, which we weren't able to explain, at least these spots that people are picking up are probably the excrement of bees."

But as far as the government is concerned, those things which Meselson et. al. can't explain loom larger than the bee theory itself. Their scientists have acknowledged that bees may be involved with the story--perhaps pollen is being used as a carrier for toxins, one has speculated to Science. But in general, the samples of leaves and rocks carry toxins in levels rot naturally found in Asia, the refugee reports, the Soviet gas mask--along with intelligence reports--have convinced the State Department and some highly reputable scientists that the Soviets are up to mischief.

"The whole body of other evidence contradicts the speculation that people are being bombed with bee droppings," says one ranking State Department official who is following the issue. His views reflect the chorus of official denunciation and rejection that followed Meselson's disclosure, that included one scientist who tested samples for the government and labelled the finds "childish" and "absurd."

"Many other governments have this view, as well as most scientists who have taken the time to study the issue," adds the government official, who insists on anonymity. "There are only a few who are entirely skeptical."

It's no surprise that the government protest over Meselson's hypothesis has been loud and local. If the Harvard scientists' suspicions are right--and it is proved that the yellow rain charges are false--U.S. credibility with its allies will be severely damaged, given the insistent public position it has taken in the past two years that the Soviets are guilty. Conversely, it's been alleged that much of Meselson's commitment to the issue is equally political; Meselson has been said to be unable to face up to the terrible fact of blatant violations of the treaty he worked so hard to achieve.

For his part, the scientist will have nothing to do with such assertions. Acknowledging his involvement with the 1972 treaty, he states, somewhat testily: "I have never let it compromise my standards of accuracy. And in fact it's the other way around. It's the fact that my standards of accuracy are offended by sloppy evidence and proper analytical work that I think it's worthwhile to devote time to this. A better job could be done."

That is the crux of the matter in his view: a lack of conclusive proof for the charges against the Russians. Three conditions, he believes, must be met if one wants to prove chemical warfare--consistent, specific reports from refugees; a definite, clear idea of what chemical is being used; and the discovery of a spent or unspent munitions containing the chemical agent involved. Seven years after reports started filtering into the West that biochemical weapons may be in use in Asia. Meselson says, none of these conditions have been filled to his satisfaction--none, he emphasizes.

Meselson doesn't deny that chemical warfare involving trichothecenes carried in bee pollen may the going on. But he gives some other scenarios that might explain the situation in the war-torn area. Maybe, he suggests, chemical warfare not involving trichothecens, where bees, frightened by the airplanes carrying an agent, go out and defecate. Or perhaps bees are alone responsible for the spots known as yellow rain. Finally, he speculates, maybe the rampant disease in the area--combined with the long-standing reports and superstition about the use of chemicals in war dating back to the middle of the Vietnam War--have caused refugees to mistakenly allege that chemical warfare is being waged.

Whatever the real scenario, Meselson emphasizes, right now he sees the situation as "the worst of both worlds." If the allegations are wrong, the U.S. is simply delaying the day it can help the people of Southeast Asia solve their natural problems, as well being embarrassed by being wrong. If the allegations are correct--as the State Department believes--then a serious violation of two international agreements will have been perpetrated (not only the 1972 treaty, but also the 1925 Geneva Protocol). Substantiated allegations, many observers believe, call into question the whole idea of arms control, as well as the reliability of Soviets to adhere to treaties.

Actually, while acknowledging that proof of chemical warfare would make it difficult to conclude arms control agreements, Meselson expresses skepticism with the assumptions of this last, commonly held view. "You don't conclude agreements with Russia because you trust the Russians. That's not the way you make these agreements. You do it because you can detect violations," he says. "The converse of that argument is that if only the Russians are innocent of this we can trust them? That's not the way to do treaties. It never was. It never is, It's a phony argument. That's not the point. The point is if they're really doing this, we ought to get it stopped."

Yet, as Meselson makes clear throughout a 30-minute interview in his office at the Fairchild Biochemical Laboratory, he has not yet in the least reached the point of pronouncing guilt on the Russians. His research will go "on the basis of hard fact," he stresses, before breaking off the interview under a deluge of phone calls and impending appointments. The task is now to further analyze the "yellow rain" spots under the microscope as well as other experiments. But Meselson, who at 53 has been a full professor at Harvard since 1964, leaves little doubt about where he thinks the research is going to end up.

"I think that what's going to happen is that very large parts of this story--maybe all, or maybe half--but large parts are going to unravel," he confidently asserts. The government, he says, "will be turned out to be wrong."