In another day - and how long ago it seems - the hope was to get the genie back into the bottle. Today the nuclear genie is at large in every corner of the globe, and the task is to try to make sure that the limits are nuclear energy rather than nuclear weapons.

Fortunately, leadership in the task of containment has been assigned to Gerard Smith, who has exceptional qualifications for what looks, on the face of it, to be an impossible undertaking. Smith knows probably more than any other individual outside the science orbit about the complexities of the nuclear process and what that process means when translated into the fantastic weapons already in existence, under construction (e.g., the trident submarine) or on the drawing board.

He directed the prolonged negotiations that resulted in the SALT I treaty signed by President Nixon in 1972. That treaty banned defensive antiballistic missiles and put a five-year limit on any increase in offensive missiles. The deadline expired in October, as U.S. and Soviet negotiators struggled to reach a SALT II agreement aimed at a pause in the nuclear arms race.

The patience and preseverance that it took in month after month of negotiation to get a treaty that the Senate finally ratified, Smith is showing in his new job. Traveling from country to country with the title of ambassador-at-large, he is well aware of the difficulties and the contradictions that lie in the path. Yet he is firm in his belief that sense will ultimately prevail and that the number of nuclear powers will be confined to the present six.

The Club of Six includes India, which set off a nuclear explosion in May 1974. The Indians say it was for peaceful purposes, but the American view is that anything that goes bang is a potential if not an actual weapon.

It takes determined optimism to believe the club will not be enlarged. The pessimistic view is that at least five new members will have qualified in the next decade. One and perhaps two have already secretly qualified or are on the verge of doing so.

Nationalistic rivalries are strong motivating force. When India set off a bomb, neighboring Pakistan immediately felt threatened by nuclear weapons in possession of an ancient enemy. The Pakistanis immediately began dickering with France for purchase of a nuclear fuel reprocessing plant, which in this game is the works. With a political upheaval in Pakistan the deal was temporarily in abeyance, although the report now is that Paris has forwarded the blueprints to the Pakistanis.

The great obstacle to containment is the fast breeder reactor, a process whereby uranium multiplies to provide an ever-increasing volume of plutonium either for nuclear power reactors or weapons. President Carter has been put on notice by Comptroller General Elmer B. Staats that he cannot legally phase out the Clinch River fast breeder reactor under present law, but only if Congress amends the law. Recently Congress put $80 million for Clinch River in a supplementary appropriation.

That will be taken as a sign by other nations that they can go ahead and follow the American example - which will make Smith's task even more difficult than it is.

The French are adamant in their determination to proceed by the fast-breeder route. We have no oil, limited coal and no uranium, they say, and that leaves us no choice but to go ahead with a method providing essential fuel for development of reactors to produce nuclear energy.

One of the stickiest problems Smith faces is the West German deal with Brazil for a complete nuclear fuel cycle. It involves up to $10 billion for completion. Smith has visited both countries and thus far seen little response to his argument for worldwide restraints. Carter has just signed a bill putting a cap on the export of nuclear fuels, and that is a step toward the controls expected to come out of negotiations currently going on among 44 nations.

Although no official in any capital has said so publicly, it is generally accepted that Israel has atomic bombs. They are believed to have been developed from enriched uranium obtained surreptitiously from a nuclear plant in Pennsylvania. Ever since the '60s Americans, including members of congressional delegations, have been denied access to the Israeli nuclear reactor facilities at DiMona.

One of the challenges Smith gets when he travels is this: Your friend and ally Israel has nuclear weapons it obtained through its own facilities after it had obtained enriched uranium. Why do you want us to forego the same privilege? A reasoned answer gets down to the terrible hazard that would follow if nuclear weapons were allowed to proliferate unrestrained.

Chasing the nuclear genie is a never-ending pursuit. It leads inot all the intricacies of science and world politics a force that holds the balance between life and death.