WASHINGTON — As President Barack Obama tries to regain control over the health care debate, one challenge is holding together the massive roster of organizations that support an overhaul of the system, or at least some parts of it.

While the half-dozen or so major groups that actively oppose Obama's efforts share common themes of free-market, anti-tax advocacy, the hundreds of groups that put their money and names behind the overhaul effort are harder to label. Some have been at odds in the past and could turn on one another as congressional negotiators try to hammer out legislation this autumn.

These diverse supporters agree that the federal government should help pay for more Americans to get health coverage and help contain health care costs.

However, they don't agree on whether the federal government should offer a public alternative to private insurance, whether nonprofit regional cooperatives might work better, or what concessions Obama should give doctors, drug makers or insurers in exchange for their support.

Many also have direct financial interests in the outcome.

Supporters include groups with names such as PhRMA, AHIP, SEIU, AMA and AARP. Others are Health Care for America NOW, Americans for Stable Quality Care, Divided We Fail, Better Health Care Together and Partnership for Quality Care.

Here's a look at who's behind them and what they want:

PhRMA: The trade group for the nation's drug and biotech firms could spend $150 million selling its message. It's led by former Rep. Billy Tauzin of Louisiana, a Democrat-turned-Republican and a longtime chairman of the House Energy and Commerce Committee.

The group committed to providing $80 billion in cost savings over a decade if an overhaul is enacted, including halving the drug costs for seniors in the current "donut hole" coverage gap under Medicare Part D. The price of PhRMA's support was that the Obama administration wouldn't use Medicare's leverage to negotiate lower drug prices or import drugs from Canada to reduce prices here.

"I can't speak for the White House, I can only tell you that, in the beginning, when we were asked to be partners in health care, we said we'll do everything that we can to help, but the line in the sand for us is price controls," said senior vice president Ken Johnson. "We really passionately believe health care reform has to happen, we really believe there has to be shared sacrifice."

PhRMA hasn't taken a stand on a public option, but it opposes driving people currently insured by employers out of the private system.

AHIP: America's Health Insurance Plans, which also sponsors a group called Campaign for an American Solution, doesn't support the public option and says it wants "bipartisan" reform.

Insurers want the government to mandate coverage for all Americans. To accomplish that through private insurance, AHIP would agree not to deny coverage for pre-existing conditions and not to base premiums on health status or gender.

However, AHIP spokesman Robert Zirkelbach said, "The only way that works is if everyone participates in the health care system." AHIP supports tax credits or other assistance for people who make too much money to qualify for Medicaid but can't afford coverage on their own.

SEIU: The Service Employees International Union has 2 million members and bills itself as the largest, fastest-growing labor organization in North America. It has 400 staff dedicated to the pro-overhaul campaign and has spent upward of $10 million, said its health care chairman, Dennis Rivera.