The most powerful southern California earthquake in seven years struck early today at the edge of the Mojave Desert, knocking out power, lighting fires, shattering windows and, in the process, exciting legions of seismologists.

The earthquake, which measured 6.0 on the open-ended Richter scale, caused only minor injuries and temporary inconvenience, authorities reported. Its 2:21 a.m. jolt was felt as far away as Las Vegas and Lake Havasu City, Ariz., to the east, and from San Diego to the San Fernando Valley just north of Los Angeles.

Scientists here at the California Institute of Technology and elsewhere on the West Coast celebrated the chance to study a major quake on a stretch of the San Andreas fault system dotted with sensing devices placed in anticipation of just such an event.

Tom Heaton, a seismologist with the U.S. Geological Survey (USGS) here, said the area 12 miles northwest of Palm Springs where the quake was centered is part of a complex "gap" in the San Andreas system where there had been no major temblors since 1948. The stretch of shifting continental plates affected today, called the Banning Fault, appears to run in two widely separated lines, like a divided highway, with many complex geological structures that the sensing devices will help illuminate.

Earthquake scientists now theorize that quakes occur in cycles, and are most likely to hit at "gaps" where a fault has not recently broken. Today's temblor was the largest in southern California since a 1979 Imperial Valley quake that measured 6.4 on the Richter scale. A 6.5 magnitude quake in the San Fernando Valley in 1971 took 65 lives. A 6.5 quake destroyed much of the downtown area of the Central Valley town of Coalinga in 1983 and killed one person. The 1906 San Francisco earthquake, which predated development of the Richter scale, has been calculated at 8.3 magnitude.

Every increase of one number on the scale, which measures ground motion as recorded by seismographs, indicates a tenfold increase in magnitude.

Riverside County officials said they suspected that a $75,000 fire that gutted a glass shop in Palm Springs this morning was caused by a quake-ruptured gas pipe. About 100,000 homes in the area lost power in the early morning hours because of downed lines, and officials asked residents to limit use of air conditioners today as they attempted to restore the system in 100-plus-degree heat.

A landslide cracked a bridge on state Hwy. 111, main route into Palm Springs, and rock slides temporarily closed highways 62 and 74 in the desert.

Two pumping stations were closed on the California aqueduct, which brings Colorado River water to southern California, and officials were forced to dump up to 1 billion gallons of water into the desert. Minor flooding resulted.

An underground section of the aqueduct ruptured at a siphon station near Interstate 10, creating a leak at the rate of 3.3 million gallons a day. While workers rushed to repair the damage, the Los Angeles Metropolitan Water District, which supplies water to 6.5 million people, cut its water flow to 25 percent of its normal rate.

Caltech seismologist Kate Hutton reported that she is usually awakened by a telephone operator when a southern California quake trips the university's sensors. But this quake, even with an epicenter 100 miles away, was strong enough to wake her on its own, an event rare enough to force her quickly out of bed and into her car for a dash to her laboratory.

Caltech researchers dispatched to the quake site found that the ground where the fault crosses Hwy. 62 near Desert Hot Springs had slipped five to six centimeters, a significant shift, USGS seismologist Heaton said. As expected, more than a dozen aftershocks hit the area, the largest of them 4.0.

USGS electronics technician Charles Koesterer said additional sensors were rushed to the area to measure aftershocks and other data. Scientists analyze earthquake formations by studying magnitude and timing of shocks from the same earthquake as measured by seismographs scattered about the area. Hutton said that there was no indication of any foreshocks or other warnings of today's major quake.

Authorities reported some minor injuries from falling debris. Capt. Nick Padilla of the Riverside County sheriff's office said an inmate at a minimum-security prison in Banning was so frightened by the quake that he jumped through a window, severely cutting a finger.

Officials said one motorist was slightly injured after his car hit a boulder on Hwy. 243 near Banning.

Palm Springs Police Lt. Lee Weigel said five people were admitted to hospitals complaining of chest pains they said were caused by the quake, and 10 people were treated for sprained wrists "from falling out of chairs or beds.