The Washington-based transportation consultancy firm, De Leuw Cather, has won a key appointment as coordinators to Southeast Asia's most ambitious transportation project to date, the $2.38 billion Singapore Rapid Transit Railway.

De Leuw Cather's partners in the project will be Wilbur Smith and Associates, headquartered in South Carolina, in a joint venture under terms not yet disclosed. The initial two-year contract is estimated to be worth about $5.5 million and when announced recently, ended a fierce international contest between five transportation companies invited by the Singapore government to tender bids.

The two U.S. companies have already worked closely together on the 2 1/2-year Athens metro project. Although the winning companies were not exactly dark horses, they were not the favorites -- Freeman and Fox Associates, who teamed up with U.K. Partners, were because of their leading role in the Hong Kong metro, which began operation in the late 1970s. The second British consortium bidding was Mott Hay and Anderson together with London Transport International Services and Halcrow International Partnership.

The remaining competitors were the French engineering consultancy Sofretu, which has been involved in a study of design options for the Singapore system in partnership with Parsons Brinckerhoff of New York, who beat both De Leuw Cather and Wilbur Smith in the bid for the third-phase preliminary study here. Mott Hay was also a participant in the phase-three study. Wilbur Smith and Associates had completed both the first- and second-phase studies.

In the light of Singapore's expressed intention to absorb as much technical know-how as possible during the project, it is ironic that the De Leuw Cather-Wilbur Smith bid appointed as subconsultants Chicago-based Louis Klauder (for the design and specification of trains), and Harry Weese and Associates (present architectural consultants of the Washington Metro system). In their competing bids, Parsons Brinckerhoff, Sofretu and Freeman-Fox had invited Singapore firms to join in their respective bids to the government as a tacit acknowledgement of the political sensitivity of the local economy to the role of foreign firms.

Not surprisingly, immediately after the announcement that the four American companies would be the key consultants, the Singapore government announced approval for an extension of its 5 percent preferential margin plan to local contractors.

De Leuw Cather will have as many as 20 of its employes on the joint venture team in Singapore for two- to three-year contracts.