The Air Force is studying a nuclear-powered cruise missile that could fly low all the way from the United States to the Soviet Union to escape radar detection.

Such a missile would be a significant advancement over the short-ranged cruise missiles President Carter has decided to build for the 1980s despite the alarms sounded by Soviet officials.

Although this advance missile, called ICCM for intercontinental cruise missile, is still an idea rather than a decision to build such a weapon, the Air Force interest gives a glimpse of what could become a new weight on the super powers' "balance of terror."

A cruise missile is like a small plane without a pilot. It flies its H-bomb to the target by "feeling" its way along with radar beams that compare features on the ground with the map stored in its mechanical brain.

Right now the Pentagon is developing two different curise missiles, the "Alchem" for air-launched cruise missile and the "Slickem" from a submarine.

In hopes of soothing Soviet fears about this new weapon designed to penetrate any defense the Russians could build in the 1980s, U.S. negotiators at the ongoing strategic arms limitation talks (SALT) have offred to limit the range of the air-launched cruise missile to about 1,500 miles and the sea-launched one to 360 miles.

However, these range limits would remain in force only through 1980. Air Force "blue sky" planners are looking at a cruise missile with virtually unlimited range for the 1990s. Such a weapon could be launched from the ground in the United States rather than depend on planes or submarines to carry them part way to their targets.

"Propulsion concepts shall consider nuclear," the Air Force's flight dynamics laboratory at the Wright-Patterson base in Dayton told defense contractors in inviting them to submit designs for the intercontinental cruise missile.

"Flight scenarios shall consider supersonic, low-altitude penetration as well as other alternatives," continued the Air Force in the guidance set forth for contractors in the Aug. 8 issue of the government publication "Commerce Business Daily."

One idea being explored is to build a hybrid missile - one that would zoom aloft on rocket power and then maneuver though the sky on a tiny airplane engine like present-day cruise missiles.

Backers of this concept said the rocket launch would keep the weapon from being destroyed on the ground by a sudden enemy attack while the slower flying afterward would enable it to be recalled afterward like a manned bomber.

The Air Force's interest in an intercontinental cruise missile marks a return to a 1950s concept which lost out to ballistic missiles now dominating the nation's land-based strategic offense.

The thinking back then was that only manned or unmanned planes could carry the heavy H-bombs of that era from the United States to the Soviet Union.

One unmanned plane of that era - an early long-range cruise missile - was called Snark. It crashed off Florida so many times in flight tests that wags called the waters "Snark infested."

With the arrival of the lighter, suitcase-sized H-bombs, ballistic missiles took over from the Snark and other cumbersom cruise missiles. Today, cruise missile engines are much smaller and more efficient than the ones tried on Snark - once again putting cruise missiles into contention for the strategic role of carrying H-bombs to Russia.

Small nuclear engines, pursued by the Pentagon in the 1950s and 1960s and then abandoned as impractical for bombers or missiles, also have fresh appeal as evidenced by the Air Force's expressed interest in them for a global cruise missile.