The Brookings Report, or Proposed Studies on the Implications of Peaceful Space Activities for Human Affairs , was a study carried out by the The Brookings Institute on behalf of NASA in 1960. The study focused on mankind's exploration of space and of the implications of the discovery of extraterrestrial life.
Of particular importance in the report was the conclusion that the discovery of extraterrestrial life could lead to the destruction of human society. Other people have labeled this process of destruction as 'the conquistador effect', whereby a primitive race who comes in contact with a technologically superior race is either destroyed or assimilated, as the Spanish did to the natives of the new world or as the whites did to the natives of North America. In a nutshell, the conclusion in the report was that a cover-up of the discovery of extraterrestrial life might be needed in order to forestall the destruction of human society.
My personal favorite part of the study is the section on the speculation that an advanced or superior race may want very little to do with us. If this were the case it would limit the knowledge we could obtain concerning them. Taking it further, if by chance certain factions of the U.S. government do know that UFOs are extraterrestrial, they may not know much else.
The Brookings Report