Moscow stood in virtually total diplomatic isolation today as the Security Council completed its third day of debate on the destruction of a South Korean airliner by Soviet warplanes, with more than 30 countries denouncing the act as unjustifiable.

As the council met, representatives of the United States and seven allied nations worked behind the scenes to complete a draft resolution that would reflect the outrage of the international community. The text is also expected to call for a U.N. investigation of the incident, for reparations to the families of the 269 people who died in last Thursday's disaster and for an assurance that Soviet military procedures will be altered to prevent a similar tragedy in the future.

American representative Charles Lichenstein said the precise content of the resolution remained "up in the air."

He expressed hope that it would be put before the council by Thursday or Friday.

Other countries involved in the drafting were South Korea, Japan, Canada, Australia, Britain, France and the Netherlands.

Some of them suggested that the resolution might not condemn the Soviet Union outright, in hopes of attracting maximum support among the 15 council members. The Soviets, however, are expected to veto any text that blames them for the incident or demands compensation.

Of the more than 30 speakers in the four council meetings held thus far, only East European countries such as Poland have defended the Soviet action. Representatives from Western, African, Asian and Latin American countries have been almost unanimous in declaring the Soviet action indefensible, although some have conceded that unanswered questions continue to trouble them.

Several Third World delegates, while calling on the Soviet Union to accept the consequence of its actions, also appealed to both superpowers not to turn the incident into an East-West confrontation. Nigeria's O.O. Fafowora, for example, after saying that "it is incomprehensible that a civilian plane on a routine flight should have been so wantonly destroyed," suggested that the incident was symptomatic of a much deeper malaise.

The superpowers appear to have embarked on confrontation and on a collision path, he said, "thereby posing a grave danger not only to international peace and security, but also to the very existence and safety of ordinary men, women and children throughout the world, who simply want to live in peace."