The Senate plunged into debate over legislation to fund the government while cutting of money for the new health care law, with both sides accusing the other of threatening to bring about a government shutdown.

Senate Majority Leader Harry Reid (D.Nev.) opened debate by denouncing the bill passed by the House Friday that embodies conservatives’ campaign to “defund Obamacare,” as the health law is known.

“Inside the House Republican bubble, the crowd cheered a plan to deny health insurance to tens of millions of Americans or else shut down the government,’’ Mr. Reid said at the outset of a debate that is expected to stretch into next weekend before any significant votes are taken. ‘President Obama has been clear. I have been clear. Any bill that defunds Obamacare is dead on arrival in the Senate.’’