WASHINGTON -- An effort by House Republicans to highlight problems with President Barack Obama's health-care law by bailing out a program for people with pre-existing medical conditions appeared to backfire Wednesday.

GOP leaders postponed a scheduled vote after the measure met strong opposition from two directions: from conservative groups resistant to any federal role in health care and from Democrats who objected that the Republicans planned to pay for the high-risk patient program by raiding a disease-prevention provision the administration has said is essential to the overhaul.

The legislation, a departure from usual GOP efforts to kill the Affordable Health Care Act outright, also faced a White House veto threat.

Erica Elliott, spokeswoman for Republican Whip Kevin McCarthy of California, said in a statement, "We had good conversations with our members and made a lot of solid progress" on the bill. But she said there was "still work to do," and with members leaving for the Bush Presidential Library dedication, "we'll continue the conversations" when the House returns in May after a recess next week.

The GOP bill would provide up to $3.6 billion to shore up the Pre-existing Condition Insurance Plan, or PCIP, which is intended to be a stopgap measure for uninsured high-risk patients until the end of this year, when full consumer protections under the health-care act go into effect.

Under the plan, those who have been uninsured for six months would be subsidized so they could buy insurance at average rates. The original goal was for the plan to reach more than 300,000 before it disappeared at the end of this year, but the program's costs were higher than anticipated and it enrolled slightly more than 100,000 before the administration announced in February that it would stop taking new applications.

Republicans sought to use their new "Helping Sick Americans Now Act" to point out defects in the pre-existing conditions program.

Their bill, said Rep. Michael Burgess, R-Texas, is a "needed piece of relief for the hundreds of thousands of Americans who were promised by their president that they would be covered under the Affordable Care Act's Pre-existing Condition Insurance Plan and then were told as of Feb. 1 of this year, 'Sorry, we're closed."'

Money for the plan would come from the Prevention and Public Health Fund, a provision of the health-care law that Republicans have assailed as a slush fund for Health and Human Services Secretary Kathleen Sebelius. Republicans also are critical of the use of $300 million from that fund to publicize the new health-insurance markets coming this fall under the health-care law.

"We want to stop Obamacare and that's why we're going to the fund, the slush fund, that Secretary Sebelius is using for the implementation of the bill," House Majority Leader Eric Cantor, R-Va., said.

The White House, in its veto threat, said the legislation would effectively eliminate funding for three years for a program that "supports critical investments such as tobacco use reduction and programs to reduce health-care-associated infections and the national burden of chronic disease."

Health and Human Services, in its breakdown of the prevention program, said among its allocations in 2012 were $91 million for immunization, $60 million for tobacco use prevention and $146 million to support community-level efforts to reduce chronic diseases such as heart disease, cancer and diabetes.

The Club for Growth and Heritage Action, which carry weight among some conservative lawmakers, came out against the measure, saying it didn't do enough to stop the intrusion of the federal government into health care.

"Fiscal conservatives should be squarely focused on repealing Obamacare, not strengthening it by supporting the parts that are politically attractive," read a statement from Club for Growth.

Democrats said repealing the broad health-care overhaul remains the GOP objective. The Republicans, said Democratic Whip Steny Hoyer, D-Md., were doing "everything in their power to make sure it doesn't work. ... They are destroying the tracks that have been constructed to give Americans health-care assurance."

Jeffrey Levi, executive director of Trust for America's Health, a group that has criticized the Obama administration for using prevention fund dollars to publicize the benefits of the new law, said the prevention account is not being misused as a slush fund as Republicans allege.

"The bulk of the funding in the prevention fund has indeed gone to the original intent of public health and prevention," he said. He said his organization, a nonprofit that focuses on promoting public health strategies to prevent disease, was opposed to the GOP bill, calling it a "foolish trade-off."

Democrats pointed out that the Republican bill would take about $800 million more out of the prevention fund than would be needed to keep the high-risk insurance plan going. They have suggested sustaining the program through the end of the year through such means as raising tobacco taxes or rolling back oil and gas company tax breaks.