Amtrak signed a $9 million contract yesterday with Breda Costruzioni Ferroviarie, an Italian manufacturing firm, to assemble up to 294 subway cars for the region's Metrorail system over a three-year period.

Under the contract, which marks Amtrak's first venture into transit-car assembly, the newest generation Metro cars will be assembled at Amtrak's heavy maintenance facility in Beech Grove, Ind. The plant, which employs more than 1,000, is used by Amtrak primarily for the maintenance and overhaul of its passenger rail cars. It also was used to rebuild old Amtrak equipment and, most recently, to renovate 15 subway cars for New York's transit system.

Breda has received two contracts totaling about $275.3 million for the manufacture of the cars from the Washington Metropolitan Area Transit Authority. The first cars will be delivered in March or April 1983 and be put in service in the fall, WMATA General Manager Richard Page said at a press conference yesterday. He said the new cars will be used on one of two as-yet-unopened lines: either the Yellow Line between Gallery Place and National Airport or the Blue Line extension to Huntington.

The subway cars will be completed at the rate of eight per month, with the last delivery scheduled for March 1986.

As prime contractor for the cars, Breda is subcontracting almost 60 percent of the components to U.S. manufacturers, who will send them to Beech Grove for final assembly. The Metro car shells will be shipped from Italy to the United States through the ports of Baltimore, New Orleans or Cleveland on their way to Indiana and will arrive in late December. Breda will be responsible for a final inspection after assembly.

W. Graham Claytor Jr., president of the National Railroad Passenger Corp.--Amtrak's formal name--said the primary objective of the contract was to be able to maintain a quality work force at the Beech Grove facility so that Amtrak's own maintenance and overhaul needs could be met. The contract will save the jobs of 50 workers who were to be laid off.

Additionally, the agreement was an important step in Amtrak's continuing diversification program aimed at developing assets and reducing its dependency on federal funding, Claytor said.

"To the extent that we can do the work and make a good profit, that is additional income and cuts down on money we have to ask Congress for," he noted. For the occasion, the head of the federally subsidized rail system was wearing a tie with "capitalist tool" printed all over it.

Because the federal government is financing 85 percent of the cost of the cars, the assembly work has to be done here by law. WMATA said the cars will look like the current Metro operating fleet, produced by Rohr Industries, which has since ended its transit manufacturing activities. But engineering improvements to propulsion, braking and electronic systems on the inside will improve reliability and help lower operating and maintenance costs, WMATA said.

Production of Breda's subway cars has been delayed because of a lengthy but recently settled strike at a Pittsburgh brake manufacturing company. Page said yesterday Breda and the transit system haven't yet been given a revised schedule for delivery of the brakes