A major effort to keep the crisis over Cuba from exploding into a nuclear holocaust is now under way at the United Nations, where Acting Secretary General Thant is conferring with American, Russian and Cuban officials, seeking to make arrangements for possible diplomatic talks that might even end in a summit meeting. In doing so he lives up to the great tradition set by his predecessor, Dag Hammarskjöld, and to the principles of the United Nations Charter. His exertions are all the more welcome because both sides have expressed their desire for negotiations. And they are all the more necessary because, while there is a temporary lull in the storm, the storm is by no means over and may at any moment  get far worse.

  On just what basis the negotiations are to be held is still unclear. The soviets continue to rush completion of their nuclear missile bases in Cuba to threaten the United States and the whole Western Hemisphere. The United States does and must continue the blockage to stop further shipments of nuclear arms. We must also continue to insist that the bases themselves be removed.

  Mr. Thant has advanced his own proposal to freeze the crisis, involving the voluntary suspension both of the blockade itself and of further arms  shipments to Cuba. But this proposal, though in keeping with his neutral status, suffers from the same effect that afflicts other superficially "even-handed" proposals, including the one to end all nuclear weapons tests by Jan. 1, 1963. They fail to provide the necessary safeguards against cheating by the aggressor.

  Premier Khrushchev is only too pleased to "accept" both Mr. Thant's proposal for an uncontrolled moratorium on Cuba and the neutralist's proposals for an uncontrolled moratorium on nuclear tests. The United States can accept neither for the simple reason that we have learned through harsh experience that we cannot trust the Soviet Union.

  Nevertheless, the United States recognizes and shares the worldwide anxiety in both cases and is doing its utmost to remove the causes. The President agreed to preliminary talks with Mr. Thant on Cuba, and we continue to search for agreements on nuclear testing. While the Soviets plant secret nuclear missile bases in Cuba, the United States has long tried to retard proliferation, by refusing to give nuclear information even to our oldest ally, France. While the Russians have a record of arbitrarily breaking off the test moratorium, forcing us to resume testing, the United States has been persistently been trying to end the poisoning of the atmosphere by a firm treaty banning all tests in the atmosphere, under water and in outer space-the only ones producing fallout-even without further controls.

  In both cases the United States must insist on controls where its security is concerned. That is why we require dismantling of the Soviet bases in Cuba under independent verification. That is why we must insist on at least a limited control for still unidentifiable underground tests, until the time (perhaps not for distant) when they can be distinguished from earth tremors and thus self-policed.

  The unfortunate fact is that we do not and cannot trust the Soviet Union we can take nothing on their word or on faith. The Cuban experience only emphasizes the point.