Democratic lawmakers in Congress are girding for a major battle over Medicare in 2009 that could result in substantial changes, including cuts in payments to private insurers that offer Medicare coverage and a new right for the federal government to negotiate drug prices. Pressure to act on Medicare is rising as the program grabs a growing share of the federal budget. Medicare spending hit $431.5 billion in 2007, nearly doubling in just seven years, according to the trustees of the Medicare trust funds.