Apparently, the U.S. government operates a DC-9 (or Boeing 717 or
similar) aircraft which is painted in light blue and white and bearing
the words "United States of America" much like Air Force One. I saw
this airplane departing runway 31 at LGA on Wednesday August 4, 2004,
at around 13:50.

Who does it carry?

Actually "Air Force One" is not a specific plane. Isn't it whichever
plane is currently in use by the President? It's a reserved call sign,
not a specific plane.

Yes, that is correct, which ever plane carries the president is called AF1.

yes, and in some exceptional situations a plane can cease to be air
force one instantaneaously in mid-air, as in when Gerald Ford was
sworn in. At the time Richard Nixon was on board an airplane whose
call sign was "Air Force One." When Ford finished taking the oath, the
pilot requested a new call sign.

Normally, though, there are two 747's that take turns being Air Force
One. They are identical in design, inside and out.

What you saw was undoubtedly a C-9.  This is a military version of the
DC-9 which was primarily used for aeromedical missions for which it
would be painted with the Red Cross insignia.  However a small number
were used for carrying officials, and were then painted similarly to
AF one.  They weren't assigned to a specified individual, but were
used primarily for cabinet level officials on official business.

ac67, thanks. very interesting. I wonder who was here.

techtor, sorry to jump to the rating. first-timer mistake.

I just heard that the first lady and the Bush twins were in town that
week. I guess then the C-9 might have been Mrs. Air Force One.

Hello Jccjr,
Your apology is accepted. I had my answer pulled out though since it
was dissatisfactory. Also, I guess you've found the answer yourself,
so I assume there's no need to have this answered. You may cancel the
question if you desire.