A showdown is shaping up among Democrats as abortion foes press House leaders to change the health care bill to explicitly ban abortion funding, or at least permit a floor vote on the issue.

The effort led by Bart Stupak of Michigan and Daniel Lipinski of Illinois could have far-reaching implications for the fate of the legislation when the House takes up the health care overhaul late next week.

Stupak, who has been at the forefront of a group of several dozen anti-abortion Democratic dissidents, said he would likely vote against a rule providing for floor action on the health care overhaul bill if party leaders do not come his way.

“I’ve got to have somewhere to responsibly express my opinion and that of my district,” Stupak said.

House Majority Leader Steny H. Hoyer of Maryland points to the abortion disagreement as perhaps the most important unresolved issue as he prepares to move the measure to the floor.

Stupak said he would look for ways to work with Republicans, if necessary, and moderate senators including Bob Casey of Pennsylvania to override the decision by House Speaker Nancy Pelosi , D-Calif., to omit an outright ban on abortion funding from the legislation she unveiled Thursday.

The anti-abortion Democrats want to win language that would essentially extend the existing abortion funding ban known as the “Hyde amendment” to the new and expanded programs that would be created by the health care overhaul. The language for the current abortion funding ban was developed by the late Rep. Henry J. Hyde of Illinois (1975-2007).

Mindful that abortion is a politically divisive issue within her caucus, Pelosi and her leadership team have sought to promote a compromise, but the anti-abortion Democrats consider it to be too weak.

The compromise language is similar to current restrictions on the use of federal Medicaid funds. The provision would ensure that federal dollars are kept in separate accounts when they flow into health insurance plans, and that federal accounts could not be used to fund an abortion.