U.S. government scientists at the California Institute of Technology have alerted their superiors to increases of radon gas which may warn of impending Southern California earthquakes.

Levels of radon, a natural gas which can be detected in well water and in the ground, have risen prior to earthquakes in China and the Soviet Union. Scientists here see a connection between a previous radon increase and a 6.6-magnitude quake in California's Imperial Valley two years ago. Ground water levels, another suspected earthquake sign, have also risen dramatically in recent weeks in some parts of Southern California.

Scientists at Caltech and at the U.S. Geological Survey in Menlo Park, Calif., said today the numbers of radon sensors are too few and studies of the gas too rudimentary to allow them to predict a quake. The radon rise, they said, may indicate an increase in strains within the earth which could produce a quake, yet any temblor could occur hundreds of miles from the most active radon sensors, 50 miles north and 25 miles northwest of Los Angeles, and near Santa Barbara.

"This increase is quite dramatic and unprecedented, but we really don't know if it means anything or not," said James Dieterich, program coordinator for earthquake prediction at the U.S. Geological Survey office in Menlo Park. A memo by two survey scientists, Thomas H. Heaton and Carl E. Johnson, to their superiors in Reston said: "Despite our present confusion about the significance of these recently reported geophysical anomalies, it seems clear that if a large earthquake were to occur in the near future, then many would claim that there were abundant examples of precursory phenomena."

Caltech physics professor Thomas Tombrello, who has been working with visiting professor Mark H. Shapiro on the radon project, said that concentrations of the gas in monitored wells at Lake Hughes near Lancaster and at Lytle Creek near Glendora rose significantly at the beginning of August. The radon levels in both wells hit a peak, subsided, and then peaked again about five days later. The level of radon was higher during the second peak than the first. Radon levels at other monitored wells have not changed significantly, a puzzling phenomenon that occurred in earlier radon buildups that seem connected with earthquake activity.

Increased radon levels have also been noted by Prof. Arthur Sylvester of the University of California at Santa Barbara, who has been taking measurements with dry sensors in the ground.