The nation's nuclear power industry took its first domestic orders of the year yesterday when Westinghouse Electic Corp, sold two nuclear plants to Commonwealth Edison Co. of Chicago.

Worth somewhere between $1.5 billion and $2 billion, the two plants will be located in Carroll County, ill., about 150 miles west of Chicago near the Mississppi River. Each plant will generate 1,150,000 kilowatts. The first plant is due to start up in 1987, the second in 1988.

The two plants are the first to be ordered this year by the Electric power industry, which has held back from nuclear plants because of the nationwide debate over nuclear power.

In 1977, four nuclear plants were sold to domestic electricity companies, all of them by Combustion Engineering co. The two largest producers of nuclear power plants, Westinghouse and general Electric Co., dis not take a single order last year.

Commonwealth Edison Chairman Thomas G. Ayers said the utility chose to build two new nuclear plants instead of coal-fired plants because it believes it costs less to operate on uranium than on coal.

"All costs considered, our existing nuclear plants generate electricity at a total cost of 30 percent less than low-sulfur coal," Ayers said. "Our fuel expense alone last year was $280 million less than it would have been if we had used western low-sulfur coal.

If oil had been used, our fuel expense would have been $680 million higher."

Commonwealth Edison relies more on nuclear power than any other electricity company in the United States, producing and estimated 45 percent of its electricity from uranium. It now has seven nuclear plants in operation generating more than 5 million kilowatts of electricity. The two plants ordered yesterday will bring its nuclear electricity to 65 percent of its total when they are built.