I assume you're referring to the Majority Leader and Minority Leader. There are two because there are two major parties; each party chooses its own leader, with the party that holds the majority of seats selecting the Majority Leader.
There are no minor leaders in the senate because to be in the senate you have to be at least 30 years of age.
house & senate leaders
Their senate.
the senate leadership in the claosely paralles leadership in the House, but the senate has no speaker.
Andrew Johnson.
House leaders have more organizational control over the actions of representatives than Senate leaders do.
The Majority and Minority Leaders have the real power in the U.S. Senate. The Vice President of the U.S. also have a lot of say in the U.S. Senate.
Floor Leaders are leaders of their political parties in each of the houses of the legislature. In the United States Senate, they are elected by their respective party conferences to serve as the chief Senate spokesmen for their parties and to manage and schedule the legislative and executive business of the Senate. http://en.wikipedia.org/wiki/Floor_Leader
As of April 2011 - the leader of the US Senate is Senator Harry Reid (D)
through public elections
-Congress, House of Representatives, Senate
harry reid