WASHINGTON, D.C.: American Airlines and its pilots' union reached a tentative agreement on a new contract Wednesday that is vague in the fine points but clear in its determination to avoid a crippling shutdown that would affect 20 percent of the nation's travelers. The contract, negotiated in seclusion on Orcas Island, Washington, will be presented to the union's board on Friday for approval. Captain Michael Cronin, the pilot's chief of legislative affairs, declined to give details of the agreement, saying, "We want our board of directors to hear it from negotiators and not from the press." The pact came as a surprise. When talks finished on Tuesday, an emergency board appointed by President Clinton to resolve the dispute was readying a report about the issues still separating the two sides. While this appears to be the end of the crisis, Cronin said there is still work to be done before it can be ratified. "Principles have to be translated into words that people can be held to," he said.