In a major victory for Boeing Co., the World Trade Organization sided with the American aviation giant yesterday in finding that European countries have provided billions in illegal subsidies to chief competitor Airbus.

The preliminary ruling by the Geneva-based WTO, although expected to be challenged by the European Union, could begin to shake up the $3.2 trillion global market in new jetliners, in which Airbus has overtaken Boeing. The next shoe to drop will be a decision that may well go the other way: The international trade body will rule next year in an Airbus challenge to what it sees as unfair U.S. government support for Boeing.

Yesterday's decision confirms a complaint by the United States, filed in 2004, that "all Airbus aircraft have received illegal subsidies and that these have caused material harm to Boeing," said Rep. Norm Dicks (D-Wash.), who was among those briefed by U.S. trade officials on the yet-to-be released decision.

Another Washington state lawmaker, Democratic Rep. Jim McDermott, said, "We learned in a WTO ruling that Airbus has enjoyed an unfair competitive advantage over Team Boeing for decades."

Boeing is headquartered in Chicago but has extensive plane-building operations in the Seattle area. Lawmakers from other states with links to Boeing, also confirmed the decision.

The WTO finding was the first step in a process that could take years to produce a final result.