In a notable policy shift, the United States has begun to spotlight and denounce more vigorously what it sees as the growing capacity of Soviet forces to wage chemical and perhaps biological warfare.
Secretary of State Alexander M. Haig Jr. opened the new approach with his allegation in West Berlin Sunday that Soviet-backed forces have been using chemical warfare in Southeast Asia. On Monday the State Department provided further details of the "physical evidence." The new emphasis reflects:
1. Washington's desire for an additional anti-Soviet propaganda weapon to counter the propaganda mileage Moscow has gained from President Reagan's reluctance to begin early disarmament negotiations. Charges of chemical warfare are an emotional "weapon" used both by Western nations and by communist countries such as North Korea and Vietnam.
2. A changed official atmosphere in Washington where investigations that may incriminate the Soviet Union can be pursued more vigorously. There is less concern now to play down accusations that might undermine American-Soviet relations.
3. A heightened concern about the arming of Warsaw Pact troops in Europe with chemical weapons, and their high degree of preparedness should chemical warfare be used against them. Secretary Haig, a former NATO commander, is well acquainted with this problem. American military officers are eager to press ahead and learn as much as they can about chemicals Moscow may already have used elsewhere -- so that defenses for use by American troops can be devised.
The charges by Secretary Haig in his Sept. 13 speech in West Berlin stopped short of directly accusing the Soviet Union of violating such agreements as the 1925 Geneva Protocol covering chemical warfare and the 1975 Biological Weapons Convention.
But he nonetheless minced no words in saying that "at the very time when the United States is being accused of delay on arms control, others appear to be violating one of the oldest arms control agreements -- that prohibiting the use of toxins."
Secretary Haig noted continuing reports that the Soviet Union and its allies have used chemical weapons in Laos, Cambodia, and Afghanistan. Most significantly he added the United States now has "physical evidence from Southeast Asia which has been analyzed and found to contain abnormally high levels of three potent mycotoxins -- poisonous substances not indigenous to the area and which are highly toxic to man and animals."
He said the evidence would be forwarded to United Nations experts. Tass responded promptly Sept. 13 by terming his allegations "unfounded and false."
State Department spokesmen say that Vietnamese forces fighting Khmer Rouge insurgents in Cambofia are believed to have used a Soviet-made and supplied poison named trichothecene.
There have long been reports that Vietnamese- and Soviet-backed government of Laos was consolidating control by dropping some kind of poisonous gas or powder on US-backed Hmong hill tribesmen. But doctors and other scientists investigating refugee accounts could not get samples of any such weapon or confirm that it had the described effects.
Campaigns by the Soviet-backed Vietnamese Army near the Thai border have provided more evidence. Refugees entering Thailand from areas of fighting have described the weapon and its effects and International Red Cross medical teams have examined survivors.
The Thai Army also has gained information by interrogating Vietnamese defectors. Khmer Rouge civilians and soldiers have told journalists and others of the alleged weapon and its effects.
This past spring, boxes of "fresh" samples, including contaminated water, vegetation, and the results of tests on humans were sent to Washington.
"The symptoms among the Cambodians were the same as those noted earlier in Laos," one expert was quoted as saying. "But it was a lot easier and faster to get active samples out of Cambodia than it was out of Laos."
A variety of reports suggested the weapons might include cyanide and a variety of Soviet-supplies shell-delivered gas called "CH." But the most important was trichothecene, the mysterious yellow powder dropped from planes and known in Southeast Asia as "yellow rain."
The most complete public study on the subject is the book "Yellow Rain," to be published in October. Its author, Sterling Seagraves, traces the origin of trichothecene to a poison developed in the Soviet Union 25 years ago. The toxin was indirectly derived from a living fungus that produces a deadly poison.
Mr. Seagraves, who remains controversial, compared gassing allegations in Laos. Afghanistan, and Laos -- all countries where the Soviet Union intervened to support governments or factions in civil war situations. He concluded that accounts of chemical warfare and its affects were all strikingly similar.