After starting the clock on a historic vote on health care reform, House Democratic leaders are running out of time to address the concerns of conservative members who are threatening to blow up the bill unless it prohibits federal funding for abortion.

Rep. Bart Stupak, D- Mich., said Wednesday there was "no agreement yet" after discussions with the White House.

Stupak has remained engaged in discussions despite leaving Capitol Hill this week after the death of his mother-in-law.

"I have had some serious conversations over the past few days with the White House and House Leadership and I will continue to make every attempt to resolve the issue of public funding for abortion," he said in a written statement.

"However, there is no agreement and I will oppose bringing the bill to the floor until an amendment can be offered or language agreed that will prevent public funding for abortion," he said.

House Democratic leaders want to pass a health care bill later this week. They cleared the way Wednesday for a floor vote on health care as early as the weekend. Publication of the changes started a 72-hour legislative clock, meaning that a floor vote could take place as early as Saturday.

But the changes did not include language addressing concerns over abortion funding, disappointing Stupak.

"I will continue to oppose and will continue whipping my colleagues to oppose bringing the bill to the floor for a vote until there is satisfactory language to prevent public funding for abortion," he said.

Stupak says he has enough votes to block the legislation. But with the clock running out and with Stupak not expected to return to Washington this week, House leaders will have to address the abortion issue behind closed doors or risk a vote over the objections of abortion foes in their own party.

Republicans voiced dismay at the prospect of Democratic leaders dealing with abortion without giving advanced notice.

"If Speaker Pelosi intends to address critical issues like taxpayer funding for abortion in the rule, they should make it available for the American people to read for 72 hours," Michael Steel, a spokesman for Minority Leader John Boehner, said. "Transparency means putting the whole bill online for 72 hours. The question now becomes: will Democrats break their pledge of transparency by making last-minute backroom deals on vital issues such as abortion?"

Fox News' Chad Pergram contributed to this report.