The U.S. Transportation Department said on Friday it would approve a transatlantic alliance between British Airways and AMR Corp.'s American Airlines if competitors can get enough access to London's Heathrow airport. 

The department said final approval of the partnership and another between UAL Corp.'s United Airlines and British Midland was dependent on reaching a new, more open, aviation trade pact with Britain. 

The United States said it would propose the divestiture of 238 weekly slots at Heathrow airport, allowing a total of 17 daily round trips by competing U.S. airlines. 

The Transportation Department said 224 of those weekly slots should be given up at Heathrow by British Airways and American. 

The alliances seek antitrust immunity to allow the partners to closely coordinate their schedules and ticket pricing. 

Only four carriers can fly directly between Heathrow and U.S. cities -- British Airways, American, Virgin Atlantic VA.UL and United. 

A handful of big U.S. airlines, including Delta Air Lines and Northwest Airlines, have vigorously opposed the closer American and British Airways alliance. 

They have asserted that stronger ties would hurt competition on lucrative routes between the United States and Europe.