WASHINGTON — Former President Bill Clinton knows just how high the political stakes are in the fight to overhaul America's health care system.

His failed attempt to revamp the delivery of medical care contributed to the Republican takeover of the House and Senate in 1994.

Fast forward to 2009, where health care's white-hot spotlight now shines on the Senate. Clinton is still in the picture, and he was expected to speak to Senate Democrats about health care legislation during their weekly caucus today, officials said. They spoke on condition of anonymity because they were not authorized to discuss his schedule.

President Barack Obama wants to sign the legislation into law by the end of the year. But abortion opponents in the Senate are seeking tough restrictions in the health care overhaul bill, a move that could roil a shaky Democratic effort.

Sen. Ben Nelson, D-Neb., said Monday he could not support a bill unless it clearly prohibits federal dollars from going to pay for abortions. Nelson is weighing options, including offering an amendment similar to the one passed by the House this weekend.

The House-passed restrictions were the price Speaker Nancy Pelosi, D-Calif., had to pay to get a health care bill passed, on a narrow 220-215 vote. But it's prompted an angry backlash from liberals at the core of her party, and some are now threatening to vote against a final bill if the curbs stay in.

Obama said the legislation needs to find a balance.

"I want to make sure that the provision that emerges meets that test — that we are not in some way sneaking in funding for abortions, but, on the other hand, that we're not restricting women's insurance choices," Obama said in an interview with ABC News.