“Behind the scenes, high-ranking Air Force officers are soberly concerned about the UFOs. But through official secrecy and ridicule, many citizens are led to believe the unknown flying objects are nonsense. To hide the facts, the Air Force has silenced its personnel.”
Supposedly he made the above statement to congress in 1960. I saw it in Leslie Kean's UFOs: Generals, Pilots, and Government Officials Go on the Record, who attributes it to a New York Times article. I also saw it presented without a source in The New Yorker article "How the Pentagon Started Taking U.F.O.s Seriously." I want to know if there's a credible source for the above statement, or if someone just made it up wholecloth and falsely attributed it to our first CIA director.
As a follow up, if the statement was indeed made by him, why would the first Director of Central Intelligence ever make such a statement? What sort of context do I need to understand why this statement was made? How do historians tend to treat seemingly incredible statements like this from seemingly credible public officials?
I've seen two entirely different sourcings for this quote. One (given from multiple webpages) is the quote was entered into Congress on August 22, 1960 (like here). I went through the entire 100+ pages of the Congressional Record for that day twice (both House and Senate) and saw nothing even remotely similar to the quote. (There's no OCR scan and handy search feature, so I can't be 100%, so you're welcome to check it yourself. The first page references "aliens" but that's the immigration kind, not the space kind.)
The other sourcing comes from the UFOlogist Michael Swords in his book UFOs and Government, who, when discussing Hillenkoetter mentions him saying to Donald Keyhoe (author of The Flying Saucers are Real) "the Air Force has constantly misled the American public about UFOs". Swords considers the quote to have a "weak source" and was unable to verify it, and only included it because he got it from a MUFON UFO Journal article in 1979 and he considers the editor Richard Hall reputable. This is, to be frank, weaker than weak -- there's no particular compelling reason to believe the quote is real other than hope, especially given the double-sourcing (which is always suspicious).
As far as what to do when an official who has "insider knowledge" says something provacative, well, we need to apply all the usual history methods of analysis and be aware the quote may have been taken out of context, or they may not have been telling the truth. I think a pretty good example of this one is the infamous
Did we know we were lying about the drugs? Of course we did.
from a quote by John Ehrlichman about the Nixon administration. The quote ends up not matching at all with what we know about the Nixon administration's handling of drug policy; it should also go without saying a convicted perjurer isn't a reliable source.
As far as Hillenkoetter, he has always attracted interest amongst UFOlogists as he was a high-level name that got connected with NICAP (the National Investigations Committee On Aerial Phenomena) after his stint as CIA director. Unfortunately, it doesn't seem like he did or said much (that's verifiable, at least) and we also have a fairly well-known fraud connected with his name: the Majestic 12 papers.
The Majestic Twelve papers were a set of supposedly Top Secret papers from the 80s put forward by the UFO researcher Willliam Moore indicating a group under Truman and led by Hillenkoetter, and connected with a supposed alien craft crash at Roswell. The papers have been pretty roundly debunked (amongst other issues, the roster of alleged members doesn't make sense, and Hillenkoetter has his name written wrong, as Adm. Roscoe H. Hillenkoetter, when at this time he used his proper title of Rear Admiral). The intrinsic desire amongst UFO conspiracists to attach things to Hillenkoetter means one's automatic reaction to a quote of the nature you mention ought to be suspicion.
Additionally, it isn't like military people have roundly denounced UFOs entirely, the recent Pentagon-released videos being a case in point. All of them have also been fairly thoroughly debunked, but by camera and special effects experts, which the military do not necessarily hire for this sort of thing and they can be fooled by camera artifacts that appear like rotating shapes just like the rest of us.