WASHINGTON  Efforts to overhaul the health care system have moved ahead rapidly, with the insurance industry making several major concessions and the chairmen of five Congressional committees reaching a consensus on the main ingredients of legislation.

The chairmen, all Democrats, agree that everyone must carry insurance and that employers should be required to help pay for it. They also agree that the government should offer a public health insurance plan as an alternative to private insurance.

But members of Congress are just now turning to the most explosive issues, which could delay or derail the process.

They have yet to tackle the question of how to pay for coverage of the uninsured.

They have not wrestled with vehement Republican objections to the idea of a new government-run insurance plan, competing directly with private insurers.