PARIS, April 11 - A deadline to take action before the World Trade Organization came and went Monday, with the United States and the European Union instead saying they would try again to agree on what constitutes acceptable government aid to Airbus and Boeing, the trans-Atlantic rivals.

The brinksmanship of the last few days apparently spurred both sides to make a further effort to avoid leaving the outcome of the multibillion-dollar dispute to the W.T.O. But neither side budged an inch in what has become a steadily nastier feud.

The newest effort to negotiate leaves Airbus in limbo as to when it might apply for roughly $1.3 billion in loans for its possible new long-distance, midsize aircraft, the A350, which is intended to compete against the 787 Dreamliner that Boeing has already put into development. The Boeing plane, which has already signed up a few customers, is scheduled to enter service in 2008.

"As long as no action is taken - action at the W.T.O. or the disbursement of aid - there is a window of opportunity to negotiate," said Claude Veron-Reville, a spokeswoman for the European trade commissioner, Peter Mandelson.