The battle for public opinion over health care intensified further on Thursday when a strange-bedfellows coalition including drug companies, doctors and a big labor union, all favoring an overhaul, opened a $12 million television advertising campaign directed at 12 states.

The advertisements are intended to counter the sharp criticism of President Obama’s overhaul efforts that has emerged at town-hall-style meetings. Change, they say, would have a positive effect.

Over soothing piano music, the narrator in one commercial tells viewers that change would mean that they could not be denied coverage for pre-existing conditions or be dropped from their plans if they get sick, and that they could still make their own medical decisions, in consultation with their doctors.

“So what does health insurance reform really mean?” the narrator says. “Quality, affordable care you can count on.”

The commercials are running in Alaska, Arkansas, Colorado, Indiana, Louisiana, Maine, Montana, Nebraska, Nevada, North Dakota, South Dakota and Virginia. They are aimed at bolstering moderate and conservative House Democrats who need some ammunition to counter the intense campaign against revamping the system. Another objective is to win over senators from swing states or whose votes are in play.

The new commercials followed by a day the opening of a 20-state, multimillion-dollar network television campaign by the United States Chamber of Commerce to try to derail support for a government-run health insurance option. Such an option, which is a provision of overhaul bills approved by three House committees and the Senate health committee, could make consumers’ premiums cheaper but would most likely take business away from private insurance companies, which the chamber represents.

The chamber’s commercial portrays Washington’s efforts at overhaul as so expensive that they would all but break the national bank, adding to the deficit and prompting a tax increase.

The new coalition is called Americans for Stable Quality Care. Its biggest financial backer is the Pharmaceutical Research and Manufacturers of America, or PhRMA, which represents the pharmaceutical industry and has promised to spend up to $150 million in advertising on behalf of Mr. Obama’s effort to change the system.

The coalition also includes the American Medical Association, Families USA, the Federation of American Hospitals and the Service Employees International Union, which represents health care workers.

Most of these groups, especially the drug companies, worked against President Bill Clinton’s proposed overhaul in 1993-94. They are generally allied now in advocating change, although they differ in some of the particulars, including the contentious matter of a public option, which organized labor supports but which the hospitals, doctors and drug companies oppose in varying degrees. The public option is not mentioned in the coalition’s commercials.

The groups in the coalition were brought together by the White House in its continuing effort to broker deals bringing them on board with the president, although he has yet to back a specific plan.