WASHINGTON -- Democrats and a handful of Republicans rebelled against the government funding bill Thursday, with a possible government shutdown looming just hours away.

Republican leaders insisted that they would not let the government run out of money at midnight, and would pass a stop-gap measure if a deal could not be reached in time.

The inelegantly named "cromnibus" appropriations bill would fund the government after current funding expires at midnight. But Democratic lawmakers revolted against the must-pass legislation because it includes riders that would gut campaign finance rules and undo provisions in the Dodd-Frank Wall Street reform act designed to curb risky trading at the heart of the 2008 financial crisis.

Trouble started in the morning when the House barely cleared a procedural hurdle to advance the bill, 214 to 212. GOP leaders managed to convince just enough of their unhappy members to stay in line, but 17 Republicans nonetheless spurned their own leadership, angry that the bill isn't conservative enough.

After the rule scraped by, the White House issued a statement urging passage of the omnibus bill, while also asking for the removal of special interest riders. But it did not issue a veto threat -- a move intended to sway some Democrats to support the bill's final passage, especially the 70 Democrats who voted with Republicans to pass a similar Dodd-Frank provision last year.

The White House also expressed disapproval of a short-term funding measure for the Department of Homeland Security, which is funded under the omnibus through Feb. 27, 2015.

Despite its reservations, the White House statement made clear that President Barack Obama would sign the omnibus bill if it clears Congress.

But as the day dragged on, no agreement was reached, and House leaders delayed a final vote on the bill. Meanwhile House Speaker John Boehner (R-Ohio) and the White House each were reaching out to lawmakers seeking to change minds. White House Chief of Staff Denis McDonough was dispatched to a meeting in the evening with Democrats.

House Minority Leader Nancy Pelosi (D-Calif.) seemed to sense the measure was in deep trouble, and sent a "dear colleague" letter to her members in the afternoon, urging them to stay united against the bill in spite of the White House's support.

"It is clear from this recess on the floor that the Republicans don’t have enough votes to pass the CRomnibus," Pelosi wrote. "This increases our leverage to get two offensive provisions of the bill removed: the bank bailout and big money for campaigns provision."

But she also signaled her members could vote their consciences. "However you decide to vote in the end, I thank those who continue to give us leverage to improve the bill," she said. "Stay tuned."

Shortly before McDonough arrived, Rep. Nita Lowey (D-N.Y.), the ranking member of the House Appropriations Committee, told reporters she doesn't know how she'll vote. Lowey helped craft the cromnibus and voted for the Dodd-Frank provision last year.

"You'll have to ask the Republicans," she said on her way into the closed Democratic caucus meeting.

Rep. Maxine Waters (D-Calif.), the top Democrat on the Financial Services Committee and a key architect of the revolt against the omnibus bill, said she launched her own whipping operation and told members not to be intimidated by the White House.

"We're fighting anybody who is lobbying for this bill," she said.