After years of decline in the number of railroad casualties, safety experts fear that a recent upturn in deaths and injuries may continue as trains begin to roll across an extensive commuter rail network planned for Southern California.

Transit officials plan aggressive public education campaigns before their latticework of commuter rail lines connects Los Angeles with five outlying counties within the next four years.

Their aim is to avoid accidents such as those that resulted in four deaths and 13 injuries on the Metro Rail Blue Line between Long Beach and Los Angeles during its first six months of operation.

While railroad education programs receive widespread applause, many safety experts worry that a surge in accidents is inevitable along new commuter rail lines. It takes time, they say, for risk-taking motorists and pedestrians to realize that light rail and other commuter trains move faster and whiz by more often than familiar, slow-moving freight trains.

"It sounds fatalistic, but we are going to see accidents going up," said Donald Costan, administrative manager of the state Office of Traffic Safety in Sacramento, who coordinates a statewide public education campaign. "It is simply because people are not used to seeing trains coming across their streets."

A recent report by the state Public Utilities Commission underscores the concern. Its statistics show that collisions on light rail lines statewide boosted the overall number of train accidents in 1989 after years of decline. Preliminary figures for 1990--expected to be released in several months--suggest that the upswing continued last year, the report's author said.

Although concerned about the trend, transit officials point out that the 35 deaths in 273 accidents at public railroad crossings statewide in 1989 represent a minuscule problem compared to the 5,381 killed in hundreds of thousands of highway accidents that year.

Transit authorities hope to relieve automobile congestion and reduce highway accidents with 412 miles of commuter rail lines to be operating by 1995 on existing tracks connecting Los Angeles, Orange, Riverside, San Bernardino, San Diego and Ventura counties.

Transportation planners say the rail network should remove the equivalent of 23,000 cars from overloaded Southland freeways.

"We would like to run our trains with no accidents, but that particular downside is far outweighed by taking 23,000 people off the freeway in rush hour," said Dana Reed, chairman of the Orange County Transportation Commission.