Not all presidents are briefed equally on the UFO issue. Carter, Bush Sr. and Reagan are listed as being the most informed. Clinton was rumored to have said "I know it's real…they won't tell me a damn thing."
I don't know about W but the head of Obama's transition team, John Podesta, went public in 2002, calling for the government to end UFO secrecy. More about these statements at:
http://www.coasttocoastam.com/shows/2008/11/16.html#recap
As for Obama's personal interest, I think he has his hands full here on Earth as illustrated during a debate when Tim Russert asked Sen. Obama about his belief in the existence of life beyond Earth:
"I don't presume to know. What I know is there is life here on Earth, and — and that we're not attending to life here on Earth."
If the time comes, however, that Obama needs a UFO advisor and taking into account his "team of rivals" approach, I have a suggestion he start vetting Dennis Kucinich who
according to (Shirley) MacLaine, saw a UFO in the 1980s while visiting the actress at her home in Washington state.
I didn't know Dennis hung out with Shirley but I do know he received the Gandhi Peace Award-2002 and what other qualifications do you need to meet E.T.s?
Unless living with one counts...