BOULDER CITY, Nev. — Against the desert backdrop of the nation’s largest solar energy installation, President Obama on Wednesday assailed Republican critics of his clean energy policies as “the flat earth society” even as he sought to demonstrate his own support for domestic oil and gas production.

Before Mr. Obama spoke at the solar plant southeast of Las Vegas, administration officials previewed an executive order that the president will announce on Thursday in Oklahoma to expedite federal permits for the southern half of the Keystone XL oil pipeline to the Gulf of Mexico. Republicans derided the move as a political stunt, intended only to blunt their criticism of Mr. Obama’s decision in January to reject, on environmental grounds, a northern leg of the pipeline from Canada to Cushing, Okla.

The partisan back and forth reflected the election-year stakes as Americans’ disgust with high gasoline prices has chipped at Mr. Obama’s approval ratings in polls and given Republicans a renewed sense of his vulnerability on pocketbook issues at a time when the economy otherwise has been improving.

The president’s visits to Nevada and New Mexico on Wednesday opened a four-state trip over two days to highlight what he calls his “all of the above” agenda to foster alternative energy sources, as well as oil and gas, with federal tax and spending incentives.