By a vote of 122 to 19, the General Assembly today adopted a Pakistani resolution demanding immediate withdrawal of Soviet troops from Afghanistan. It was the widest margin of the now seven similar measures passed since the 1979 invasion.

Uganda, Burkina Faso and St. Christopher and Nevis joined the 119 nations that had voted for a similar resolution one year ago. And Mozambique dropped from the score of countries -- the Soviet Bloc and close allies Angola, Ethiopia, Syria, Libya and Madagascar -- that had opposed the measure.

Today's vote demonstrated that Third World opposition to the occupation, rather than fading with time, continues to gain momentum.

Diplomats backing the resolution expressed the hope that the continued pressure on Moscow might generate movement on the issue at next week's summit meeting between President Reagan and Soviet leader Mikhail Gorbachev.

Afghanistan is likely to provide the first practical post-summit test of Soviet and American intent on regional disputes. The U.N. mediator who has handled the issue for four years, Undersecretary General Diego Cordovez, has scheduled his next round of "proximity talks" between Pakistan and Afghanistan in Geneva starting Dec. 16.

The assembly resolution outlined a framework for a political solution -- troop withdrawal, an end to outside interference, international guarantees and the return of refugees -- and endorsed the U.N. mediating role. It did not mention the Soviet Union by name.

In a report issued before the assembly debate, Cordovez conceded that a procedural impasse had been reached in August. The Afghan government insisted that a timetable for Soviet troop withdrawal could only be discussed in direct talks with Pakistan. Pakistan said indirect talks, with Cordovez shuttling between the two sides, should continue -- otherwise, Pakistan would have granted de facto recognition to the Kabul regime without the assurance that Soviet withdrawal would ensue.

Officials close to the talks suggested that one side would "blink" on procedure when the underlying dispute between Washington and Moscow is resolved.

The Soviet Union has refused to offer a timetable for withdrawal. Last month, participants in the talks said, the United States told Cordovez that until a timetable is given, it could not comment substantively on a document guaranteeing Afghanistan against outside interference.

In a speech here Oct. 24, Reagan cited Afghanistan as one of the regional conflicts that "will be a central issue in Geneva." He called for talks between the "warring parties," to be followed by Soviet-American negotiations, but warned that until there is "definitive" progress, U.S. support for rebel forces "shall not cease."

Since then, U.S. officials have suggested that differences with Moscow over Afghanistan may not be soluble in isolation, but only as part of a "package deal" involving other regional disputes.

In this week's U.N. debate, Ambassador Vernon Walters said the United States "is prepared to guarantee a comprehensive and balanced settlement in Afghanistan predicated on a complete withdrawal of Soviet forces." But without a timetable, "no solution is possible and no guarantees can be given. Instead, the carnage and destruction will continue."

Last month, Soviet Foreign Minister Eduard Shevardnadze said here that the prerequisite for any deal is an end to "outside interference." He added, "And if there is a guarantee that it will not be resumed, it will then become possible to withdraw the Soviet military contingent from Afghanistan."