As the assassination of Archduke Franz Ferdinand heralded the beginning of World War I, so history might view the attack of US Airways Flight 1549 by Canadian geese, experts in the federal Agriculture Department indicated to the Daily News today. The Canadian-goose population has "increased fourfold since 1990," they said, and the geese are growing ever more restless. "Eventually, something is going to happen," Michael Begier, who runs the airport wildlife hazards program, warned a Board of Inquiry from the National Transportation Safety Board at yesterday's hearings on the matter. "We're very fortunate that Flight 1549 was not a catastrophe." But, he said, "It is a warning shot."