After six years of fruitless negotiations, the United States yesterday formally accused the European Community of violating international trade rules through government subsidies to the consortium that builds Airbus airplanes.

The EC, in a statement issued by its Brussels headquarters, immediately appeared to escalate the confrontation, threatening a trade war "with unpredictable consequences for the course of world trade."

At stake are competitive positions in the lucrative global market for civilian airplanes for the world's giant aircraft makers: Boeing Co., the world's leader in sales; McDonnell Douglas Corp., which is struggling; and Airbus Industrie, the European government-supported newcomer that has broken the U.S. monopoly on sales of big airliners.

U.S. Trade Representative Carla A. Hills said the United States sought a ruling on the long-standing dispute from an international panel convened under the rules of world trade, the General Agreement on Tariffs and Trade, known as GATT. If the panel supports the U.S. contention, European countries that make up the Airbus consortium would have to end subsidies or compensate the United States for as much as $237.5 million in lost business last year.

Under GATT rules, it could take six months or more for the panel to come up with a ruling.

A senior trade official said the United States, which has postponed action on the Airbus dispute since last spring, moved after the EC rejected the latest U.S. offer and came back with an "unacceptable proposal."

"This made the whole thing uglier than the previous brand of ugly," the official said.

More is at stake in the issue than export dollars. Europe has decided that a commercial aircraft industry is crucial for the jobs it produces and the technological gains that come from building and designing big jets. As a result, the United States said, the four governments that make up the Airbus consortium -- Britain, France, Germany and Spain -- have spent nearly $20 billion in subsidies to design and build the planes.

The U.S. action yesterday comes on top of a major dispute in early December over European subsidies to farmers that led to the the collapse of four years of global negotiations to strengthen the GATT rules.

Over the past two months, however, the United States and the EC appeared to be moving closer on the farm trade issue.

A senior administration trade official denied yesterday that the Airbus complaint is related to the collapse of the GATT talks. "We would do exactly what we are doing if the {talks were} in terrific shape and we had no other problems," he said.

But the official said the "common thread" linking all U.S. disputes with the European Community is government subsidies, whether to farmers or manufacturers.

While the United States has been complaining since 1985 against the full range of government subsidies for the Airbus, it brought the case to GATT on only one of them: German government payments to its member of the consortium, Deutsche Airbus, to compensate for exchange rate fluctuations that cause the value of the dollar to fall against the German mark.

The trade official said this goes directly against the GATT subsidy code. But he added the administration will likely broaden the case to include other government subsidies.