The Metro board awarded contracts to two construction companies yesterday for major projects on the subway system's long-delayed Green Line through Southwest and Southeast Washington.

The board approved a $24.9 million contract to excavate tunnels to link the planned Waterfront station at Fourth and M streets SW with a stop near the Washington Navy Yard. It also approved a $12.6 million contract for a 1,000-space parking garage at the proposed Anacostia station near Rte. I-295 and Howard Road SE.

The Green Line, the only unopened route in the Metro system, is scheduled to start service in 1990. The line's construction has been delayed by court battles, neighborhood opposition and shortages of funds.

The contract for the three-level garage in Anacostia was the focus of a protracted dispute. In April, Metro officials rejected all bids on the project, citing violations of rules requiring participation by minority-owned businesses. After a second round in July, the agency again turned down all bids, citing inadvertent technical errors by Metro officials along with further problems in gaining adequate minority participation.

In the third round, Metro and D.C. officials agreed to relax minority participation requirements from 35 percent to 25 percent as part of an effort to avoid further delays.

Yesterday the contract was awarded to Kiewit Construction Co., an Omaha-based firm that also has been hired by Metro to build the Anacostia station.

Officials said Kiewit has complied with minority requirements.

The $12.6 million bid was the lowest of four submitted in October. But the price was about $1.6 million higher than a bid rejected by the authority in April.

The contract to construct the half-mile tunnels between the Waterfront and Navy Yard stations was awarded to Harrison Western Corp. of Denver.

The company also is a partner in the firm hired by Metro to dig tunnels for the Green Line beneath the Anacostia River.

In another development, officials announced that Metro's new Italian-made subway cars will start service on the Yellow Line Nov. 17 and on the Orange and Blue lines in February. The new cars now are used only on the Red Line.