The U.S.A. government (along with other 'official' governments around
the world) is only a tool, so if I was in the U.S.A. government and
even if I was the president of the U.S.A., I can't do anything unless
I got the orders from my superiors, I assure you, it ain't the
citizens of the U.S.A.

And if the superiors said on not to react to the situation, the tools
will not react.

After all, fighter pilots will stay on the ground if they aren't
ordered, even if there's an 'emergency' situation that's going to
happen.

Fortunately, a drastic decrease of humans population isn't part of
'their' agenda, so it will unlikely to happened, even if the whole
human governments are told to come to a standstill. On the other hand,
a local impact with local ffeects probably would be allowed, only it
would be publicized in a global scale and potrayed as if it it had a
major global impact.



Now... As for the originial question, I will assume that you will use
some sort of a fictional world, much like the one in "Deep Impact",
only that unlike in "Deep Impact", astronomers around the world
suddenly just croaked, even the backyard variety and the regular
stargazer variety (amateur astronomers).

I will do the following:

- Calculate the damage that will be causes the impact itself and the
effects caused by the impact.

- Prepare on the damage control needed.

- Save as many resources (including people) as possible.

- Tell the public on the situation, progressively, as calm and subtle
as possible. Information will be given in a 'need to know' basis.

- Pray to God.