WASHINGTON (AP) -- The insurance industry Tuesday laid down a marker on health care, warning in stark terms that a proposed government insurance plan would dismantle the employer coverage Americans have relied on for a half century and overtake the system.

In a joint letter to senators, the two largest industry groups also said they don't believe it's possible to design a government plan that can compete fairly with private companies in a revamped health care market. That particular statement seemed to be aimed at lawmakers of both parties who are seeking a compromise on the contentious issue.

Release of the letter from America's Health Insurance Plans and the Blue Cross Blue Shield Association came as House Democrats pushed forward with a partisan health care bill. Meanwhile, key Senate Democrats were still laboring to achieve an elusive bipartisan compromise on President Barack Obama's top legislative priority of controlling costs and providing health coverage to 50 million uninsured Americans.

Obama's goal for signing a bill in October appears in doubt.

But Sen. Max Baucus, D-Mont., chairman of the Senate Finance Committee, is doggedly pursuing a compromise. "We will get a bipartisan agreement," he insisted Monday.

Of the five House and Senate committees working on health care, Finance is the only one that appears to have a chance at a bipartisan agreement. Baucus planned to huddle behind closed doors Tuesday with a group of senators he's dubbed the "coalition of the willing." Others involved are top committee Republican Charles Grassley of Iowa; Republicans Mike Enzi of Wyoming, Orrin Hatch of Utah and Olympia Snowe of Maine; and Democrats Kent Conrad of North Dakota and Jeff Bingaman of New Mexico.