The policy-setting board of the Metro transit authority voted yesterday to buy 75 new buses for $12.5 million from a West German-affiliated company, overriding objections from one board member who sharply criticized the firm.

"In the long run, I think it's going to cost us," warned Fairfax County Supervisor Joseph Alexander, a longtime member of Metro's board of directors. Alexander's comment came after the board approved the deal with Neoplan U.S.A. Corp., a two-year-old Colorado-based firm established and partly controlled by the owners of Gottlob Auwaerter GMBH & Co., a West German bus manufacturer.

For three weeks, Alexander, who is also chairman of the American Public Transit Association, has waged a campaign to block the purchase of Neoplan buses, contending that transit systems in Milwaukee, Pittsburgh, Rockford, Ill., and elsewhere had experienced delays and shortcomings in buses purchased from the company.

A Milwaukee transit official, in a letter made public by Alexander, described Neoplan as "totally disorganized" and added, "They had no quality control." Complaints cited by Alexander from other transit systems included "No two buses are built alike" and "Front doors have fallen off while in service."

In awarding the contract to Neoplan, the Metro board acted on recommendations by the transit authority's staff, which attributed Neoplan's troubles to the firm's recent entry into the U.S. bus manufacturing market and said the company has now taken steps to ensure "timely" and "satisfactory" bus deliveries. The new buses are scheduled to arrive in November and December.

"We had a few growing pains that are past, thank God," said Rolf Ruppenthal, a Neoplan sales representative. "We're very proud that we now have an order for the nation's capital."

European manufacturers have recently entered the American bus market, long dominated by two U.S. companies, General Motors Corp. and Grumman Flxible Corp. The European-affiliated firms include M.A.N. Truck & Bus Corp., a subsidiary of a West German company, and Volvo of America Corp., established by the Swedish auto maker. Canadian manufacturers include Flyer Industries and General Motors of Canada. One other U.S. firm, Gillig Corp., has also started producing urban transit buses.

Metro, now seeking to improve its 1,700-bus fleet, is also scheduled to receive 210 renovated General Motors buses and 33 new articulated buses, which bend in the middle.