I thought they were there to serve the public good (subject to national security concerns).
certainly not stated in their employment contracts from what I've seen. Their job duties are actually fairly well defined becoming slightly more obtuse as you get towards the directors position. Their mandate is definitely not to report to the public directly. As employees they have certain obligations and guidance for conduct, they know the consequences when they sign up.
One of the things I have always admired (so far) about the US public service is its openness with information (a lot of it free to).
This is true, but there is no talk of stopping the availability of information, simply that they want to have quality controls on what goes out. You will still be able to get reports on Energy, climate etc., what you might not see as much of is the "doom and gloom" warnings from individuals whose opinion is not held by the entirety of the USGS or NASA. What they are trying to avoid, I believe, is individuals using their positions to add undo authority to their own viewpoints. From what I've seen once the USGS as a whole has come to some conclusion on a particular topic they are quite open about sharing it.....that does take time to come to the shared conclusion as evidenced in the lag times between global energy reports.
While what rockdoc said is true, the other side of the coin is that as a registered professional geologist, or in my case a licensed environmental professional, we have already sworn to hold paramount the health and welfare of the public although we're paid mostly by private industry.
You need to be pretty careful about how you interpret the various professional codes of ethics. I know that in the case of the Alberta Association of Professional Engineers Geologist and Geophysicists that they would support you with legal assistance (no guaranty of how good this is) if you disclosed something that could be shown to directly threaten human life, property etc. and your company sacked you as a result. In this case it would have to be an almost 100% chance that it would happen (an example might be a company fails to disclose soil measurements that demonstrate considerable solifluction or slope instability in a region where they plan to construct multi-family dwellings). On the contrary if it is something that is a "well it might happen" scenario that can't be proved one way or the other (an example here might be the somewhat over the top predictions from James Hansen on climate change; another might be some wild predicitions about super volcanoes in Yellowstone and their affect on the regional populace) then you are pretty much on your own, your company/government agency could sack you and the professional body would not support you. There is a huge difference between opinion and fact.