The issue of national health insurance is back. Not the old specter of socialized medicine where doctors are salaried drones of the state and the government pays all. But a new middle-of-the-road approach designed to bridge some of the serious gaps in American health care while making sure that the $458 billion that goes into medicine every year is wisely spent.

Fueling the debate on national health insurance is the problem of 30 million to 35 million Americans who have no medical coverage and therefore cannot pay their bills if they get sick.

Predictably, the Reagan administration at first promoted a laissez-faire policy in health care, fostering competition among hospitals and doctors as a way to let the marketplace determine the cost of care and its quality.

But now a curious change is taking place in American medical politics.

To begin with, the traditional foes of national health insurance -- the American Medical Association, the American Hospital Association, the Federation of American Health Systems (a trade association of for-profit hospitals and other medical institutions) -- are not so enamored of a totally free marketplace in health care.

In order for competition to work, these health leaders say, it is not fair that one hospital should get stuck with a high proportion of indigent patients so that they end up losing money when they treat people who cannot pay their bills.

At the same time, consumer groups are lobbying federal and state governments to provide coverage for indigent Americans and increase benefits to those who have inadequate insurance.

This is creating an unusual alliance between hospital and physician organizations on the Medical Right and consumer advocacy groups on the Medical Left.

Both sides want the government to do more -- not less -- in providing health care and expanding benefits for Americans who fall through the cracks of the current system.

"The {federal} government should be the provider of last resort. It is in food and housing -- why not health care?" says Michael Bromberg, executive director of the Federation of American Health Systems. "Competition and deregulation and all the things I like won't work unless we take care of the poor."

But there's a catch. The government -- and private insurers -- also wants to keep costs down. This raises the possibility of mandated fee schedules imposed on hospitals and doctors, as well as other cost-control measures -- the traditional bane of the health-care establishment.

The Reagan administration, meanwhile, for all its emphasis on the deregulation of health care, has already dropped some of its ideological tenets in the face of economic pressures. It has, in fact, introduced what may be the most far-reaching reform in hospitals: a partial fee schedule in the form of the government's prospective payment system for Medicare.

In other countries, a mandatory fee schedule, usually negotiated between the government and the medical community, is a key feature of national health plans. Since Medicare covers only one group of patients -- the elderly and disabled -- it has a limited effect on the majority of the population. But to many health leaders, the new Medicare system is a first step toward wider government regulation of hospital and physician fees.

What's more, the debate in Congress over catastrophic medical insurance for the elderly has resurrected old arguments for a national health plan that would protect all residents in the U.S. from bankrupting medical costs. Several proposals to prevent the elderly from incurring catastrophic hospital bills are being considered, and some form of legislation is expected before the end of the year.

Although the focus has been on hospital care, congressional hearings have brought attention to other needs of the elderly, such as coverage for nursing home care and drugs. They have also provided an opportunity to look at the gaps in coverage for children and many working adults.

Meanwhile, the AIDS epidemic has become a political lightning rod. As an expensive chronic illness that can cost up to $150,000 to treat, acquired immune deficiency syndrome is already revealing shortcomings in private and public insurance plans as well as in government disability coverage. The Health Insurance Association estimates the total bill for AIDS, not including the cost of the new drug AZT and other related illnesses, will reach $40.5 billion between now and 1991 -- straining the capacity of hospitals, doctors, nurses and social workers to care for an increasing number of patients.

"The growing burden of AIDS may be what forces us to look at some type of national health insurance plan," says Dr. Howard H. Hiatt of Harvard Medical School and author of "America's Health in the Balance." "We are the only industrialized country except for South Africa that does not have universal coverage."

Yet the United States is not alone in its economic dilemma of how to provide increasingly sophisticated care to greater numbers of patients -- without breaking the bank. Escalating medical costs that drain a disproportionate share of the national budget are a worldwide phenomenon among industrialized nations. No matter what form of health care, each country is having trouble as it tries to balance the issues of cost, access to doctors and hospitals and quality of treatment.

All this is setting the stage in Congress and on the campaign trail to re-examine how well and how fairly health care is delivered -- and at what cost to patients and taxpayers.