“And I believe we are in the midst of a multidecade, secretive arms race — one funded by misallocated taxpayer dollars and hidden from our elected representatives and oversight bodies,” Mr. Elizondo said.

Mr. Elizondo is one of the country’s highest-profile government whistleblowers on UFOs, and his appearance before an on-the-record, public congressional hearing reflects the changing attitudes toward the issue. For decades, the government said hardly anything about its UFO research efforts and dismissed suggestions that some UAP might be extraterrestrial or at least may involve technologies that cannot be explained with today’s science.