He delivered hisremarks during an appearance at the National Press Club following theconclusion of the fifth annual X-Conference, a meeting of UFO activistsand researchers studying the possibility of alien life forms.

Mankind has long wondered if we're "alone in the universe. [But] onlyin our period do we really have evidence. No, we're not alone,"Mitchell said.

"Our destiny, in my opinion, and we might as wellget started with it, is [to] become a part of the planetary community.... We should be ready to reach out beyond our planet and beyond oursolar system to find out what is really going on out there."

Mitchell grew up in Roswell,New Mexico, which some UFO believers maintain was the site of a UFOcrash in 1947. He said residents of his hometown "had been hushed andtold not to talk about their experience by military authorities." Theyhad been warned of "dire consequences" if they did so.

But, he claimed, they "didn't want to go to the grave with theirstory. They wanted to tell somebody reliable. And being a local boy andhaving been to the moon, they considered me reliable enough to whisperin my ear their particular story."

Roughly 10 years ago, Mitchell claimed, he was finally given an appointment at Pentagon to discuss what he had been told.

An unnamed admiral working for the Joint Chiefs of Staff promised touncover the truth behind the Roswell story, Mitchell said. The storiesof a UFO crash "were confirmed," but the admiral was then denied access when he "tried to get into the inner workings of that process."

The same admiral, Mitchell claimed, now denies the story.

"I urge those who are doubtful: Read the books, read the lore, start tounderstand what has really been going on. Because there really is nodoubt we are being visited," he said.

"The universe that we livein is much more wondrous, exciting, complex and far-reaching than wewere ever able to know up to this point in time."

A NASA spokesman denied any cover-up.

"NASA does not track UFOs. NASA is not involved in any sort of cover-upabout alien life on this planet or anywhere else -- period," MichaelCabbage said Monday.

Debates have continued about what happenedat Roswell. The U.S. Air Force said in 1994 that wreckage recoveredthere in 1947 was most likely from a balloon-launched classifiedgovernment project.

Stephen Bassett, head of the ParadigmResearch Group (PRG), which hosted the X-Conference, said that thetruth about extraterrestrial life is being suppressed because it ispolitically explosive.