British Airways Plc and American Airlines were attacked by a rival US airline on yesterday as being less than halfway adequate.

A senior executive at Delta Air Lines said his airline was arguing with regulators that BA and American would have to give up 700 weekly runway slots at London Heathrow to make room for effective transatlantic competition at the airport.

This is twice the number of slots proposed by the European Competition Commissioner Karel Van Miert and four times the 168 slots proposed last year by the previous UK government.

But Stephan Egli, Delta's vice president for Atlantic and Pacific regions, said Delta had calculated many more slots were needed to allow viable competition on the full range of transatlantic routes at Heathrow, Europe's most important international hub airport.

"We came to a number of anywhere between 700 and 800 slots for all the other carriers,'' he told reporters at a company press briefing.

On one route alone, he said Delta wanted to be allowed to operate a rival service to New York JFK which would need at least 70 weekly slots to be viable, enough for five daily return flights against BA and American's 13 daily departures to JFK.

"The fact of the matter is unless there is at least one or two other carriers offering five or more (daily return) flights between Heathrow and JFK there is no competition,'' he said. "It will end up as a monopoly because other carriers will drop out.'' BA and American are due to resume negotiations on their alliance with the European Commission and the British competition authorities later this month.

But the two airlines have already threatened to drop the deal and with it the prospects of liberalising the Anglo-US aviation trade pact, which restricts access to Heathrow, if they are called on to surrender even 350 weekly slots.

The current Bermuda II agreement allows only BA, American, United Airlines and Virgin Atlantic Airways to operate out of Heathrow and leaves Delta and other carriers only restricted access to London's second airport at Gatwick.

On Monday Delta finally terminated a wholesale seat purchase deal to get vicarious access to Heathrow with Virgin, whereby it bought blocks of seats on Virgin's Heathrow flights for resale in the United States. Egli said that Delta had suffered "very substantial'' losses from the deal after Virgin refused to cut the price it charged Delta for the seats.