Thousands of union members walked off their jobs at the Santa Fe Railway yesterday to protest the railroad's testing of equipment that lets trains run with smaller crews.

Santa Fe spokesman Robert E. Gehrt said members of the Brotherhood of Locomotive Engineers and the United Transportation Union went on strike yesterday afternoon.

The railroad, which runs from Chicago to Texas with lines to the West Coast, continued to operate some of its freight service, with supervisors staffing some 20 trains from Chicago to Kansas City, he said. But some Amtrak passenger lines on Santa Fe tracks were forced to shut down, including the Southwest Chief between Chicago and Los Angeles and the Oakland-to-Bakersfield line. Thousands of passengers were turned away and will be given refunds, Amtrak spokeswoman Sue Martin said.

At issue is a test of "Roadrailer" equipment used on a Santa Fe train that left Chicago yesterday for a General Motors assembly plant in the Los Angeles area.

"Roadrailers" are trailers with an auxiliary set of steel wheels that allows them to run on rails, saving the weight of flat cars and reducing the number of workers required, Santa Fe President John Swartz said in a statement.

Swartz said the unions refused to go along with the test and walked off the job after learning that supervisors were used.

The unions made a "general agreement" to run with reduced crews over short distances, but the unions refused to approve the move over longer distances, Swartz said.

C.A. McDaniels, general chairman of the Brotherhood of Locomotive Engineers local in Fort Madison, Iowa, said the railroad's decision against using union engineers or train crews violated the Railroad Labor Act.