LAS VEGAS (AP) _ A Greyhound bus en route from Los Angeles to Las Vegas skidded into a barrier on rain-slick Interstate 15 early Sunday and flipped onto its side, injuring 31 people, most of them slightly, officials said.

The bus carrying 33 people and the driver was about three blocks from the Las Vegas Strip when the accident occurred around 6 a.m. during a heavy rain, said Highway Patrol Sgt. Bill Marquardt.

''The driver was heading north and started to change lanes, and apparently just lost it,'' Marquardt said.

Most of the injuries did not appear to be serious, he said.

The injured were taken to four Las Vegas hospitals, where all but one were treated and released, nursing supervisors said. A Los Angeles man was listed in stable condition at University Medical Center with fractured ribs.

Manuel A. Bispo, a Marine stationed at Camp Pendleton, Calif., said ''people started to panic'' when the bus skidded into the concrete barrier in the median of the six-lane highway, then flipped.

''I yelled 'Don't panic,''' Bispo said. ''People were shoving to get out. They were afraid the gas tank was going to blow up.

''After I yelled and another guy yelled the same, people calmed down and exited orderly,'' said Bispo.

Bispo and his wife, Marie, said the bus ran onto the shoulder of the interstate twice previously on the 280-mile trip that began at midnight.

Charlie Tibbs, a Greyhound spokesman in Las Vegas, declined to identify the driver. He said the accident was probably the result of slick roads.

There was nothing to indicate excessive speed was involved in the accident, Sgt. Bill Marquardt of the Nevada Highway Patrol said. ''The roadway was wet and slick,'' he said. ''The bus just appeared to go out of control.''