NEW YORK (Bloomberg) — AMR Corp.'s American Airlines and British Airways Plc won tentative US government permission to deepen their trans-Atlantic alliance as they counter competition created by the 2008 lifting of flight restrictions between the US and Europe.

American Airlines, the second-largest US carrier, and British Airways, Europe's third-biggest, may jointly price, market and schedule international flights in their Oneworld alliance without fear of antitrust prosecution, the US Transportation Department said on Saturday.

As a condition of approval, American and British Airways must yield four pairs of take-off and landing slots at London's Heathrow Airport, Europe's busiest, to rivals that would provide new US service, the Transportation Department said. That's a fourth of the 16 pairs of slots the department asked the carriers to give up in 2002, when an earlier request for antitrust immunity fell through.

The decision "beggars belief," said Richard Branson, president of Virgin Atlantic Airways Ltd., a British Airways competitor that had campaigned against the agreement, in an e- mailed statement. "Four slots pairs is a complete joke, and those responsible for this decision should hang their heads in shame."

The decision may become final after a 60-day comment period, the Transportation Department said.

"The potential benefits outweigh the potential harm," Susan Kurland, the department's assistant secretary for aviation and international affairs, wrote in the decision. "Oneworld could provide the travelling and shipping public with a wide range of valuable benefits, including lower fares."

Carriers restricted by law from cross-border mergers seek such grants of antitrust immunity to act more like single entities. Iberia Lineas Aereas de Espana SA, Finnair Oyj and Royal Jordanian Airlines are also part of the agreement, which is still being evaluated by the European Union.

American and British Airways also won tentative approval for a separate joint venture with Iberia, according to the Transportation Department order.

Airlines use each others' routes to expand networks and compete with other large alliances. Oneworld is the third-largest global airline alliance behind Star and SkyTeam.