PLAYING AROUND with the law on nuclear proliferation, as the Senate Appropriations Committee has been doing, is genuinely dangerous. When the committee's bill comes to the floor, the Senate needs to listen to the senators in both parties who have had experience with the international strategy -- over the decades, a remarkably successful strategy -- to prevent the spread of nuclear weapons throughout the world.

The committee is trying to work out a policy for aid to Pakistan. Ever since its rival India carried out a nuclear explosion 13 years ago, Pakistan has been working with unwavering zeal toward its own bomb. The United States has been giving Pakistan very substantial aid, but American law requires cutting off aid to any country that is building nuclear weapons. With the Soviet invasion of Afghanistan, because the supply routes to the guerrilla resistance lie through Pakistan, Congress suspended that law. But the suspension has now expired, and Congress has to decide what to do next.

What the Appropriations Committee has done is to create a huge new loophole by declaring that the cutoff will not apply to any South Asian country if another country in the region is pro-ducing plutonium -- as India does. The committee is responding to Pakistani complaints that it's not fair to prevent Pakistan from having nuclear weapons when India has, at least, the ingredients. But that kind of fairness is a formula for letting any and every country have nuclear weapons. If Pakistan gets a bomb, that would be justification -- under the Appropriations Committee's logic -- to let Iran build one.

The committee thinks that it is making the world safer with this misguided concept of regional equity. It apparently hasn't thought much about the precedent for the Middle East. Applied there, its rule would mean abandoning American sanctions against the Arab countries that want nuclear arms. Just as Pakistan cites India's advances in nuclear weaponry, the Arabs could cite Israel's.

Nuclear arms control and disarmament is going to be a subject of intense attention this week during the summit meeting here. The United States and the Soviet Union are now beginning to make progress toward reducing their formidable arsenals. But there's a little more to arms control than the U.S.-Soviet balance alone. This one unwise bill from the Senate Appropriations Committee, if it were to be enacted, would rapidly accelerate the nuclear arms race in the Third World