WASHINGTON - Moderate Senate Democrats threatened Sunday to scuttle health-care legislation if their demands aren't met, while more liberal members warned their party leaders not to bend.

The dispute among Democrats foretells of a rowdy floor debate next month on legislation that would extend health care coverage to roughly 31 million Americans. Republicans have already made clear they aren't supporting the bill.

Final passage is in jeopardy, even after the chamber's historic 60-39 vote Saturday night to begin debate.