The General Assembly overrode Soviet Bloc objections today and voted overwhelmingly to continue an investigation by a four-man panel of experts into charges that Soviet-made chemical weapons were used in Afghanistan and Indochina.

The vote was 86-20, with 34 abstentions, and only the Soviet Union and its closest allies opposed it.

U.S. representative Kenneth Adelman charged that the treaties banning chemical warfare, signed by both the Soviet Union and Vietnam, "are being flagrantly violated," and this use of toxins "has growing implications for both present and future arms control arrangements."

The U.N. panel's first report, released last month after the experts had examined American evidence and visited refugee camps in Thailand, was disappointing to U.S. officials.

The experts, from Egypt, Peru, Kenya and the Philippines, "were cautious in the extreme and did not address much of the evidence we submitted," one American diplomat said.

Despite the contention by high officials in Washington that the American data constituted a "smoking gun," the U.N. panel reported itself "unable to reach a final conclusion as to whether or not chemical warfare agents had been used."

It did say that the symptoms in some of the cases reported "could suggest a possible use of some sort of chemical warfare agents."

American officials expressed the hope that with its new mandate, the expert panel would be able to conduct more extensive interviews with Afghan refugees in Pakistan and Cambodian and Laotian refugees in Thailand.

During the U.N. debate, France raised a question about the U.N. staff's impartiality in servicing the panel, charging that its "work was delayed by the undue amount of time allotted for some of the correspondence to go through the Secretariat."

The U.N. employees involved are an Iranian and a Pole, who report to the chief of the U.N. disarmaments division, Jan Martenson of Sweden, viewed by American officials as "a cautious man who tried to steer a mid-course and offend no one."