Soviet leader Mikhail Gorbachev today repeated a proposal to halt nuclear weapons tests starting on Aug. 6, the 40th anniversary of the dropping of the atom bomb on Hiroshima.

The proposed moratorium would last until a nuclear test ban treaty is concluded, Gorbachev said in an interview with a correspondent of the Press Trust of India, his first with a non-Soviet journalist.

The interview, published today by the Soviet news agency Tass, came in advance of a visit here this week by Indian Prime Minister Rajiv Gandhi.

The Soviets attach particular importance to their longstanding ties with India and are eager to affirm that relationship with Gandhi. The five-day visit will be Gandhi's second since he took office after the assassination of his mother, Indira Gandhi, last October.

The interview was seen here as a sign of the warmth with which Gandhi will be welcomed. The published text, most of it on Soviet-Indian relations, consisted of written answers to submitted questions, but Gorbachev did meet and talk briefly with the reporter, S. Gupta.

In the interview, Gorbachev affirmed the "high level, dynamism and comprehensive nature" of Soviet-Indian relations and paid a glowing tribute to Indira Gandhi.

He also reiterated accusations that the United States is building up its military presence in the Indian Ocean and resisting Soviet efforts to turn the area into a zone of peace. He said the United States had spurned efforts to convene an international conference on the Indian Ocean and cut off bilateral talks on the issue.

On international issues, Gorbachev again challenged the United States to reciprocate the Soviet moratorium on medium-range missiles in Europe, a gesture which, he said, would put the arms talks in Geneva "on a practical footing."

The proposal for a moratorium on nuclear testing was made by two U.S. retired admirals and was endorsed last month by the presidium of the Supreme Soviet. The Reagan administration has opposed a complete ban on testing, contending that it could not be verifiable.