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President Obama said Thursday that rising health care costs represent the "biggest threat" to the financial health of the country, as he urged Congress to help him enact comprehensive reform by the end of the year.

The president spoke at the top of a White House health care summit that invited dozens of representatives of the health care sector -- including doctors, patients, insurers and drug industry employees. Obama also invited Republicans, who were expected to speak up.

He told his guests that health care reform is critical to the economic recovery, claiming that skyrocketing health care costs are forcing families out of their homes and into bankruptcy.

"The cost of health care now causes a bankruptcy in America every 30 seconds. By the end of the year, it could cause 1.5 million Americans to lose their homes," he said. "Even for folks who are weathering this economic storm, and have health care now, all it takes is one stroke of bad luck ... to become one of the nearly 46 million uninsured or the millions who have health care, but can't afford it."

He said the rising costs, by a wide margin, pose "the biggest threat to our nation's balance sheet." Obama said the costs simultaneously squeeze the federal budget, state budgets, family budgets and small businesses.

"That's why we cannot delay this discussion any longer," Obama said. "Because health care reform is no longer just a moral imperative, it's a fiscal imperative."

The White House, however, could cite no statistic to back up the claim that health care costs cause so many bankruptcies. They cited a 2005 column by a Harvard University scholar that said someone files for bankruptcy every 30 seconds in the U.S. in the aftermath of a serious health problem -- not necessarily because of health care costs, though.

Obama proposed putting aside $634 billion over the next year 10 years in his budget blueprint last month, but his administration still has to tackle how to fix the world's costliest health care system. Obama said Thursday his plan will actually help reduce the deficit over the long term.

Among the invitees are some who helped kill the Clinton administration's health care overhaul in the 1990s. Everyone is supposed to be on his best behavior, but will that last?

"This is a different day," said Chip Kahn, a hospital lobbyist who opposed President Bill Clinton's plan and was to attend Thursday's gathering. "I think among most of the stakeholders, everyone wants to see this work. There is a tremendous feeling that it's time."

Now president of the Federation of American Hospitals, Kahn worked for the insurance industry in the Clinton years.

The difference this time, Obama says, is that health care costs have become unsustainable, particularly in a sinking economy. The U.S. spends $2.4 trillion a year on health care. Obama's goal is health coverage for everyone.

Senate Republican leader Mitch McConnell of Kentucky released a letter to Obama, saying his party is ready to work with the administration on health care, but warning that reforms should not lead to a government-run system, and must balance coverage expansions with curbs on costs.

In support of Obama's efforts, liberal activists have mobilized to keep the pressure on Congress to pass legislation this year.

"It would be a mistake to dismiss this as a gabfest," Drew Altman, president of the Kaiser Family Foundation, said about Obama's meeting. "It's an effort to keep the momentum going. The details are not going to be worked in two or three hours at a White House summit."

There were concerns Wednesday about some of those details.

Senate Finance Committee Chairman Max Baucus, D-Mont., who will play a leading role in writing health care legislation, raised questions about the proposed $634 billion "down payment" for expanded coverage that Obama included in the 2010 budget he released last week.

The Associated Press contributed to this report.