Negotiators from the United States and the European Union were set for their first formal confrontation in a dispute over aid to Boeing and Airbus at the World Trade Organization on Monday, two weeks after seeking WTO arbitration. On the day the two aircraft manufacturers were also facing each other in a press conference at the Le Bourget air show in France, where each was seeking maximum impact from order announcements, US and EU trade negotiators would ask formally here for the creation of special trade dispute groups. Each group would be composed of three to five arbitrators. The United States is asking the World Trade Organization to rule against subsidies paid by European governments to Airbus. The Europeans are asking the WTO to declare US subsidies for Boeing to be illegal. Under WTO procedures, a party to a dispute challenged by another may oppose the creation of a special arbitration group. Both sides were expected to use this tactic on Monday, while also defending their points of view before the WTO dispute settlements panel. Each side may then request a new meeting within 10 days. It will not then be possible to oppose the constitution of a study group. The dispute is regarded as one of the biggest and the most complicated that the WTO has ever been asked to handle and could last until 2006 or even for many years.