The United States awarded a contract Tuesday for construction of a $36 million housing project at a U.S. military installation, indicating a treaty covering key American bases will be extended beyond 1991, a Filipino opposition leader said.

U.S. Ambassador Nicholas Platt awarded the two-phased project to construct 506 housing units at Clark Air Base, 50 miles north of Manila, to the Sundt Corp. of Tucson, Ariz., and the Filipino-owned Atlantic Gulf and Pacific Co.The contract was the first to be signed since Washington agreed last month to provide the government of President Corazon Aquino $481 million in aid in each of the last two years of the 1947 Military Bases Agreement expiring in 1991.

New negotiations will have to be held if the United States is to maintain the bases beyond 1991.

A Navy official said during Tuesday's formal awarding ceremony the construction project is the biggest to be undertaken at Clark in 30 years.

Platt said the contract was "a concrete step" in the implementation of the agreement signed in Washington last month, which substantially increased U.S. aid to the Philippines.