When President Lyndon B. Johnson signed the Nuclear Non-Proliferation Treaty 20 years ago this Friday, he called it "the most important international agreement in the field of disarmament since the nuclear age began."

Since then, 138 countries have signed the treaty, under which they agree not to acquire nuclear weapons or help others to do so.Despite this encouraging progress, enough important nations ignore the pact to make President Johnson's optimistic words ring hollow.

Among the leading holdouts are South Africa, Israel, India, and Pakistan. Each either has or is on its way to developing a nuclear bomb. Likewise, each is one of the world's major trouble spots.

Moreover, at least three nations that have signed the treaty - Libya, Iran, and Iraq - are known to be strongly tempted to violate it.

That wouldn't be hard to do. Despite its tough language, the non-proliferation treaty contains some large loopholes. Though it might submit to inspection by the International Atomic Energy Agency as required by the treaty, a signatory nation could still stockpile plutonium and develop the capability to make a bomb. In fact, Libya, Iran, and Iraq are widely suspected of having signed the treaty just to make it easier for them to buy nuclear equipment abroad.

Still other signatories have shown few qualms about supplying non-nuclear nations with sensitive equipment that could be used to build nuclear weapons.

Once a nation acquires nuclear weapons, it can either ignore the treaty with impunity or merely serve the required three-months' notice that it is pulling out of the non-proliferation pact.

Though the holdouts are becoming more isolated and more conspicuous, the pact cannot be considered a success until they are persuaded or prodded into making non-proliferation pledges. Even then, the treaty's loopholes will have to be closed before the world can rest as easily as it would like to.