Top U.S. military commanders in the Pentagon and in Saudi Arabia are considering a nuclear option for war with Iraq -- not a nuclear bomb to kill people, but a nuclear bomb to knock out all Iraqi electronic equipment.

In the early stages of a war with Iraq, a single, high-altitude detonation of a nuclear bomb would shower the land below with an electronically destructive wave known as electromagnetic pulse, or EMP. If strategically placed, EMP might shut down communications systems, missile-launch systems and any tanks or planes that rely on electronic equipment.

The seriousness of the discussions and the careful analysis going on at the Pentagon mark the first time the United States has so extensively studied the use of EMP against any target smaller than the Soviet Union.

The use of EMP against Iraq has drawbacks. It is a weapon with radioactive fallout, and it would set a dangerous and shortsighted precedent. The United States is not eager to be the first to use nuclear weapons in the volatile Middle East, a region likely to have its own nuclear arsenal in the next decade. Another thing holding back the strategists is the fact that EMP may not be precise. U.S. weapons and equipment would have to be at least 100 miles away from the target, or they could be knocked out too.

EMP is no sci-fi fantasy. It is an intense burst of energy that travels at the speed of light and hits electrical circuits with more than 50,000 volts per meter, shorting them out and shutting down all major power facilities.

The effect of EMP was discovered by American scientists in 1962 when a high-altitude atomic test knocked out street lights and power lines in Hawaii, more than 800 miles away.

Hawaii was spared a total blackout because part of its electrical grid was built on an old vacuum-tube concept, and its telephones used electromechanical relays. But today most of the world, including Iraq, has converted to solid-state electronics with microcircuits that are sensitive to EMP. One expert report we have seen says solid-state circuitry is "a thousand to a million times more easily damaged by an EMP than the older vacuum-tube technology."

One highly classified Joint Chiefs of Staff report we have seen warned that America's own military communications systems would be so thrown out of whack by EMP that the "ability to execute a coordinated strategic nuclear response to attack could become questionable."

The report said that a single Soviet bomb exploded 250 miles above Omaha could start an EMP wave that would cause power blackouts from coast to coast.

The research on EMP as an offensive weapon has lagged far behind that for other weapons, including the Strategic Defense Initiative, chemical lasers and particle-beam technology.

That's why, according to Pentagon sources, the effect of EMP in a war with Iraq is unknown. Nuclear scientists never considered the use of an EMP blast over an area as small as Iraq and Kuwait. Most of the research applies only to a blast over an entire continent.