There is no more important challenge in the world today than achieving the twin goals of reducing existing nuclear weapons stockpiles while simultaneously preventing the spread of nuclear weapons capability to ever more nations around the world.

I was the principal author, along with Sen. Charles Percy, of the Nuclear Nonproliferation Act of 1978-- a law that for the first time required all nations receiving nuclear exports from the United States to adopt "full-scope" safeguards--that is, to agree to place all their nuclear facilities under international inspection. Passage of the NNPA was inspired in part by India's use of American "heavy water" to produce the plutonium that was used in what India described as a "peaceful" nuclear explosion in 1974. Peaceful or not, the detonation violated American understandings about the legal uses to which our nuclear exports could be put.

As a result of India's refusal to adopt full-scope safeguards (indeed, most of its program is currently unsafeguarded), the NNPA requires the Nuclear Regulatory Commission to prohibit the licensing of nuclear exports to that country. President Carter overruled the NRC in connection with two fuel shipments for the Tarapur reactors in 1980. Although I led a Senate floor fight to overturn the president's decision, the fuel shipments were approved by a vote of 48-46.

The floor fight was conducted against a background that included Indian threats to remove International Atomic Energy Agency safeguards from previous American fuel shipments, as well as threats to reprocess the fuel to extract plutonium --despite the fact that American consent was legally required.

In seeking to build a more constructive relationship with India, the Reagan administration has now reportedly worked out an arrangement whereby we will not object to the French supplying fuel for the Tarapur reactors. In return, India will agree not to carry out the threat to remove safeguards in Tarapur.

On the question of reprocessing, however, Prime Minister Indira Gandhi has told The Post that, in her view, India does not require U.S. consent to reprocess any spent fuel at Tarapur. Thus, a possible major point of contention between the U.S. and India regarding Tarapur remains. In addition, our broader objectives of gaining Indian acceptance of full-scope safeguards--and the even more fundamental goal of obtaining assurances against additional Indian nuclear tests--will not be realized under this agreement. While we may have achieved a gain in U.S.-Indian relations, we must await further developments to see if it is also a gain for nuclear nonproliferation.

In any case, it is extremely important that our cooperation in obtaining an alternative supplier for India under the special circumstances surrounding Tarapur not be considered a precedent for moving us away from the provisions of the NNPA in the future.

In particular, there must be no retreat from the principle of not supplying nuclear materials--fuel, technology and equipment--to those countries refusing to accept full-scope safeguards. That principle could be strengthened in the present context if the Franco-Indian agreement regarding Tarapur fuel included an understanding that supplies would cease in the event of a nuclear detonation by the Indians, and that full-scope safeguards would be required for nuclear exports to plants other than Tarapur.

Significantly, American insistence on full-scope safeguards has not resulted in a breach of safeguards on fuel previously shipped to India--as so direly predicted by the proponents of the 1980 Tarapur sale. That should prove to the Reagan administration that steadfastness of purpose on nuclear nonproliferation is the sine qua non of successful policy.

Over the past 18 months, such determination has been noticeably absent in our dealings with other countries that have rejected full-scope safeguards. We looked the other way in South Africa, for example, while American nuclear brokers arranged shipments of non-U.S. nuclear fuel. We allowed Brazil to purchase foreign nuclear fuel without imposing the penalties of our agreement. We allowed a computer to be shipped to Argentina for use in a heavy-water plant.

We are also sending $3.2 billion in military and economic assistance to Pakistan without requiring cessation of nuclear weapons development. Finally, the administration's recent relaxation of our policy on reprocessing and the use of plutonium sends a similarly unfortunate signal to the rest of the world.

Building effective, long-term nonproliferation arrangements ultimately requires the cooperation of all nations, particularly nuclear suppliers. India and other countries have argued that no one-- especially a nation already possessing nuclear arms --can interfere with their right to pursue advanced nuclear technology, and, of course, they are technically correct. A "right"? Yes. Common sense? No.

While we try to get control of existing nuclear weapons stockpiles, it's just common sense that we do everything within our power to prevent the additional spread of nuclear weaponry. That is to the world's ultimate benefit, including India.

At issue, however, is not a vacuous philosophical debate over the right to develop destructive force. Rather, the point is that promoting world peace and reducing the threat of annihilation will not be served by wrapping even more fingers around the nuclear trigger.

India is already highly respected among Third World nations; I hope it will use that leadership role by helping to halt the global spread of nuclear weapons. I welcome the improvement in relations between our countries. I hope we can also look forward to the day when India, Pakistan and other nations join the 114 non-weapons states that have signed the Nuclear Nonproliferation Treaty. That one act would do more than anything else to build a true, worldwide nonproliferation ethic--one that our country, India and, indeed, all mankind share a common interest in maintaining.