The White House web site includes a section called We The People from which people can petition the Obama administration on issues of importance to them. According to BBC News, the White House promises to respond to any petition that gains 5,000 signatures.
One such petition called upon the US government to acknowledge the existence of extraterrestrial life and contact with human beings. The US government has now responded:
The U.S. government has no evidence that any life exists outside our planet, or that an extraterrestrial presence has contacted or engaged any member of the human race. In addition, there is no credible information to suggest that any evidence is being hidden from the public's eye.