WASHINGTON — Deep divisions among Senate Democrats over whether cuts to popular benefit programs like Medicare and Medicaid should be part of a plan to slow the government's mushrooming debt pose a big obstacle to a deal for avoiding a potentially economy-crushing "fiscal cliff," even if Republicans agree to raise taxes.

Much of the focus during negotiations seeking an alternative to $671 billion in automatic tax increases and spending cuts beginning in January has centered on whether Republicans would agree to raising taxes on the wealthy. President Barack Obama has insisted repeatedly that tax increases on the wealthy must be part of any deal, even as White House officials concede that government benefit programs will have to be in the package too.

"It is the president's position that when we're talking about a broad, balanced approach to dealing with our fiscal challenges, that that includes dealing with entitlements," White House press secretary Jay Carney said Tuesday, referring to the mammoth Social Security and Medicare programs.