It's rather the other way round. The USA pays the biggest chunk of money to the UN yearly. The United Nations are beyond any doubt US-centric.
Edit1: [This was supposed to be a reply to an earlier post. I certainly am still not used to this forum interface.]
Edit2: Fine. Let's get the facts straight. You might want to read this first of all: http://www.un.org/en/documents/charter/chapter7.shtml.
The UN was founded under one big goal - to avoid anything alike WW II and its attrocities. In order to achieve that it has evolved into a gigantic conglomeration of suborganizations, agencies, programmes and whatnot.
The Security Council presides over all issues that may threaten peace, are a breach of peace or an act of aggression.
Before the Fall of the Iron Curtain a military intervention to secure humanitarian assistance wouldn't of ever been possible. Yet - funny thing! The world changes and the UN tries to keep up with the new kind of wars that have emerged through the fall of one of the bipolar powers of the last half of the XXth century. Want to know more? - Go wiki: http://en.wikipedia.org/wiki/Neoreal...onal_relations)
A dormant committee which never came to use is the Military Staff Committee (UN Charta, Chapter VII, Art. 47). Out of reasons which go far over the topic we are discussing right now - the member states agreed on negotiating the conditions for each case that might require a military intervention. That offers a lot of flexibility for heads of state - participate (yes or no?), support (yes or no?), what kind of support?, what is the exact mandate? (border controll?, peacekeeping?, combat?) and so on...
The American troops involved in Libya aren't sent there expressively by the United States alone, but by the International Community (the United Nations). Thus no "declaration of war" from the Congress is needed. Support from Congress would be still swell. You got a budget to vote upon every year, don't you?