EDITORIAL : NUCLEAR MADNESS; PAKISTAN RAISES THE STAKES BY CONDUCTING TESTS OF ITS OWN.

MADNESS. That's the best word we can think of to describe India's decision earlier this month to conduct underground nuclear tests.

The same word applies to the response by Pakistan, India's longtime enemy, to conduct nuclear tests of its own. Pakistan, with a per capita income of approximately $2,100 a year, can no more afford a nuclear buildup than India, where the per capita income is even less - about $1,500 a year.

But crying over spilled milk won't accomplish anything. The challenge now for President Clinton and other world leaders is to find a way to prevent the crisis from escalating.

That won't be easy. Since neither side was deterred by unilateral economic sanctions by the United States, other steps must be taken. One possibility is to secure the cooperation of all the major powers, including China, to avoid doing anything to strengthen either side.

Another is to encourage India and Pakistan to follow the example set by the United States and the former Soviet Union and explore the concept of detente as a means of averting a mutually disastrous nuclear holocaust.

Neither India nor Pakistan, which fought three wars during the past 50 years, felt an urgent need to negotiate when they confronted each other with conventional arms. That should change now that they are facing the threat of war involving the use of weapons of mass destruction.