The European Union said on Sunday that there was still a period of weeks, possibly months, available to strike a deal with Washington on subsidies for their rival aircraft makers and avert a showdown at the WTO.

The United States and the EU will miss the April 11 deadline they set to reach an accord on cutting support for Boeing and Airbus, raising the prospect that they will resume the cases they made last year at the World Trade Organization.

Despite mounting acrimony over the dispute in recent weeks, both sides have expressed a willingness to negotiate beyond the deadline.

"We hope it will be possible to continue negotiation. It is of course open for both the EU and the U.S.... to refer the matter to the WTO. But in our opinion this is better avoided," said Simon Fraser, head of European Trade Commissioner Peter Mandelson's cabinet.

"It is not the EU's intention to move first on WTO action," he told reporters in Brussels.

However, an aide to Mandelson noted that an agreed standstill on fresh aid to the aviation companies would lapse with the deadline on Monday, and EU member states could not negotiate indefinitely because Airbus is expected to seek "launch aid" loans for its new model, the A350.

"Clearly one cannot allow a sort of uncertain situation to drag on for very long," the aide said. "Nevertheless, I would hope that there is a period, certainly of weeks -- possibly of months -- where we can still have some room for flexibility."

The United States warned on Friday that it would resume its case against the EU at the WTO if the bloc's member states approved a new round of government loans for Airbus.

Airbus's A350 will compete with Boeing's newest offering, the 787.

The EU has said it will not sacrifice Airbus launch aid without a balanced reduction in Boeing's support, which include federal contracts for military and space research and tax incentives in the firm's industrial heartland, Washington state.

Airbus, which is co-owned by Franco-German-Spanish aerospace firm EADS and Britain's BAE Systems, overtook Boeing as the world's largest manufacturer of big commercial jets in 2003.