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Ina U.S.-Soviet communique last Saturday, the two nations reported that "progress was achieved in bringing closer together the position of the two sides."

Gromyko repeated that claim of progress in a 90-minute address to the U.N. General Assembly yesterday, and added: "It is important now to ensure a successful completion of the [nuclear arms control] talks and without any delay."

This annual Gromyko speech, less polemical than many he has made at the United Nations in 20 years, including some criticism of the United States, but also great stress on the need for continued East-West detente, or reduction of tension.

Gromyko said "It had been stated that recently Soviet-American relations have experienced certain stagnation if not a downright slump." However, he noted, President Carter had stated his desire to develop relations with the Soviet Union, and Soviet Leader Leonid I. Brezhnevhas responded in kind.

One new public element was added by Gromyko to the Kremlin's known positions on nuclear weapons control.

He said the Soviet Union is now prepared to ban underground nuclear weapon test without waiting for all nations possessing nuclear weapons to join in. In 1963 the United States, the Soviet Union and Britain agreed to end all above-ground nuclear testing.Weapons testing was shifted underground.

"Today," Gromyko said, "We are taking one more step forward: under the arrangement of the United States and Great Britain we agree to suspend for a certain time underground nuclear weapons test even before the other nuclear powers accede to the future treaty."

Gromyko did not amplify that. U. S. officials said they were somewhat surprised by his announcement, as the three-power talks on the underground test ban are due to resume in Geneva next week.

Until now, the public position of the Soviet Union has been that China and France must join an underground nuclear test ban before it becomes effective. President Carter, in his first press conference in Febuary urged action on this issue without waiting for nations like France and China to agree.

A continuing obstacle in the American-Soviet-British talks on the test ban, however, has been Soviet insistence on an exemption to permit underground testing of "peaceful" nuclear devices, to alter the course of the river beds or fulfill other civilian purposes. U.S.-Soviet treaties now pending in the Senate for limiting underground nuclear testing permit this distinction between types of tests.

Gromyko strongly criticized the United States' development of a nuclear bomb. The neutron bomb is designed primarily to kill enemy troops while limiting the nuclear damage to property. President Carter is debating a decision on employment of neutron bombs.

This is a "merciless" and "inhuman" type of weapon, Gromyko said, "in the same category with such cruel and barbaric means of warfare as bacteriological or chemical weapons." He called for a U.N. ban on such weapons.