WASHINGTON (AP) — Last November, diplomats from Brazil to Japan joined oil and gas executives at the headquarters of Washington's largest lobbying group to christen a new partnership.

Inside the marble walls of the U.S. Chamber of Commerce, a crowd of 200 welcomed the U.S. Gas Infrastructure Exports Initiative — a coalition of 25 companies, nine trade groups, five law firms, at least five federal agencies and a nonprofit think tank. Its mission: to drive sales of American natural gas by pumping dollars into pipelines and gas-processing facilities overseas.

The initiative, coordinated in part b...