President Barack Obama will defend his proposal for a government-run health insurance option in a speech Monday before the American Medical Association, even as the idea meets growing concern on Capitol Hill.The AMA, a critical group that Obama would like to enlist as an ally, has said it will oppose overhaul plans that include a public option. Some moderate Senators whom Obama needs in order to pass a health care bill appear to be balking at proposals to include a government-run insurance plan.“The president will be clear about what a public option does and doesn’t mean for patients, physicians and our broader health care system,— a White House official said of the speech, to be delivered in Chicago. Obama will outline steps to provide health insurance for those who don’t have it, according to the official. Such steps “include a health insurance exchange where private plans compete with a public option that drives down costs and expands choice.— Health insurance exchanges are generally conceived as tools for organizing insurance plans into a type of marketplace, increasing options and decreasing premiums for those who do not have access to large employer-based plans. Obama will reiterate the point that the White House has been making to try to mitigate fears about a public option, asserting that those who are happy with their current insurance will be able to keep it. The president will also contend that the country relies too much on treatments that are expensive but not more helpful than cheaper alternatives, laying out “his vision— for a system that uses best practices and closes cost disparities.And he will discuss the about $950 billion that the White House says it has come up with to pay for the health care overhaul, including cuts in Medicare and Medicaid spending and a plan to limit tax deductions of high-income earners.