The government's two nuclear weapons laboratories are studying the possibility of a new electromagnetic pulse (EMP) bomb which, if exploded above the Soviet Union, would black out communications but not kill people, informed scientists said this week.

Scientists have known of the EMP effect from atomic explosions for years, but the new bomb would heighten that effect.

The enhanced EMP bomb is one of several special-effects weapons in which there has been new interest at the national nuclear laboratories at Livermore, Calif., and Los Alamos, N.M., since President Reagan's speech three weeks ago calling for new efforts to defeat nuclear missiles.

"It is one of the defensive systems that would hurt the enemy without necessarily hurting his people," a Capitol Hill source familiar with the program said. Another virtue, he added, is that "it is not an anti-ballistic missile system outlawed by the 1972 ABM treaty."

Other advanced nuclear effects under study, laboratory sources said, include concentrating the X-rays produced by a nuclear explosion into a kind of laser beam, and making a beam out of the so-called uranium spray from such an explosion. Some experts say it will take more underground nuclear testing than now permitted by treaty to find out if these new ideas can be turned into workable weapons.

Under a 1974 treaty the Soviet Union and United States agreed to limit the explosive power of their underground nuclear weapons tests to 150 kilotons, or the equivalent of 150,000 tons of TNT.

Although the Senate has not ratified the treaty, both Washington and Moscow since 1976 have said they are abiding by it.

The Reagan administration in February asked the Soviet Union to meet to discuss adding on-site verification provisions to that treaty, claiming the Soviets had conducted tests over the past several years that went above 150 kilotons.

Earlier this month the Soviets turned the administration down and Tuesday the Soviet Embassy released a statement calling on the United States to ratify the agreement. "Uncertainties mentioned by the U.S. side," the embassy statement said, "would not have taken place if the entire verification system established by the treaties had been put into effect."

Beginning in 1981 the Reagan administration, influenced in large part by nuclear scientist Edward Teller, has been providing additional funds through the Department of Energy for laboratory exploration of advanced nuclear weapons concepts.

Teller, a leader in building the hydrogen bomb in the 1950s, for many years has been pushing for a so-called "third generation" of nuclear weapons. The first generation was the atomic bomb and the second was the more powerful hydrogen bomb.

The EMP weapon, according to some scientific sources, is among the most promising of the new concepts and one that could be achieved sooner than could other, more exotic weapons systems. The idea would be that if a Soviet attack were launched, the initial U.S. response would be to "black out" Soviet communications, one source said, thereby immobilizing Soviet military capabilities and laying their defenses open to several forms of retaliatory strikes.

Not all scientists agree that an EMP bomb would be a step forward, however.

One former government scientist said earlier this week that the United States is more vulnerable to the EMP effect than is the Soviet Union. That is because U.S. offensive and defensive weapons are more dependent on the tiny electronic semiconductor chips that the EMP destroys.

When a nuclear weapon is exploded it produces a momentary but powerful electrical charge called EMP. The EMP can pass through a human body without damage, but it has the effect of overloading and thus breaking electrical circuits.

The EMP phenomenon has long been known to nuclear scientists as a side effect of an explosion and against which equipment has had to be protected. For example, there is an effort under way to shield B52 bombers against EMP so that they would be able to take off in the face of a nuclear attack with electronic systems still working.

In recent years, however, in looking for new weapons ideas, scientists began studying ways to intensify the EMP from a nuclear explosion.