With the new Democratic Congress promising to lower health care costs, makers of inexpensive generic drugs sense a unique opportunity to level the playing field with their brand-name rivals.

Generic manufacturers, like Barr Pharmaceuticals and Mylan Laboratories, know that sympathy on Capitol Hill will go so far. So, lobbyists are using a Bush administration threat of new regulatory fees to the industry’s advantage, arguing that Congress must first fix a patent-law loophole that favors brand name competitors.