Forty nations from the Third World introduced a General Assembly resolution today calling on the Soviet Union to withdraw its troops from Afghanistan immediately.

Pakistani Foreign Minister Agha Shahi opened the debate by warning that the Afghan crisis "threatens the very basis of the United Nations."

The Soviet intervention, he charged, "has set back the process of detente, darkened the prospects for disarmament," and "opened an ominous new chapter in the history of superpower rivalry. . . ." a

The resolution, which the assembly will vote on later this week, does not mention the Soviet Union by name. It calls for "the immediate withdrawal of the foreign troops from Afghanistan," and then for a political solution to the crisis.

It asked U.N. Secretary General Kurt Waldheim to appoint a special representative to pursue a solution including security guarantees for Moscow and Afghanistan's right to exist without outside intervention.

A similar resolution was adopted by an overwhelming vote at a special assembly session a month after the Soviet invasion last December. While it had no practical effect on the Soviet presence, it constituted, in a sense, an intergovernmental opinion poll on the Soviet invasion.

The sponsors have made the present resolution a trifle milder, and hope to win even wider support.

The Soviet reaction has been strong and harsh both in private and in public. A number of Third World diplomats say they have been privately approached by Moscow and warned that a vote for the resolution would be viewed as an "unfriendly act" -- the strongest possible warning in the language of diplomacy.