A major environmental and energy conservation program began in Milwaukee yesterday as a recycling plant which produces six times the energy it consumes went into operation.

The plant, located on the banks of the Menomonee River, will take the 250,000 tons of trash annually produced by this city of 700,000 and separate it into fuel, metals, paper, glass and other recyclables. The material will be sold to local processors.

At the dedication yesterday, Milwaukee's mayor, Henry F. Maier, said, "We are piercing the doubts of critics and we are satisfying the hopes of those who realize that token efforts at recycling cannot long sustain themselves."

The $18 million plant was built by the Americology division of American Can Co. Its 400,000 ton capacity will permit the wastes of suburban communities to be processed together with Milwaukee's, according to the manufacturer.

The primary purchaser of the city's sorted trash is the Wisconsin Electric Power Co., which has contracted to buy paper and other shredded, combustible materials as fuel to supplement coal-fired boilers used to generate electricity. Use of the refuse-derived fuel is expected to save about 75,000 tons of coal a year.

American Can has a 15-year contract to handle all municipal-collected waste in Milwaukee. The city has an option to buy the plant after the first five years of operation and share in the revenues of the sale of recovered proudcts.