At President Obama's request, Congress is rushing to produce a plan that promises both medical coverage and high-quality care for all Americans.

But nationalization of the way 250 million non-elderly Americans receive medical care should not be taken lightly. Such efforts could create relentless cost pressures and, in turn, a decline in the quality of medical care that most Americans take for granted.

Lost in the rush to action is a clear definition of the problem.

THE CASE FOR radical reform is invariably made by pointing to the Census Bureau's estimate that 47 million Americans lack health insurance. However, this estimate grossly misrepresents the size of the problem.

The number of Americans who lack health insurance is not synonymous with the numbers who lack care.

More careful analysis shows that a large percentage of the uninsured either have high enough incomes to afford medical care or receive health services from a variety of government and other sources. In a study for the Employment Policies Institute co-authored with Dave O'Neill, I found that close to half of those reported as uninsured have incomes at least 250 percent of the poverty line (averaging about $65,000) and could therefore be viewed as voluntarily uninsured.

About 30 percent report they were offered insurance by their employers but rejected it, and others qualify for Medicaid but are not enrolled.

It is frequently alleged that the uninsured are denied basic health care services -- in particular, preventive care. Data on screening for cancer show that although the uninsured in the United States do not have as high a level of testing as those with private insurance, their screening rates are as good, or better, than those of Canadians -- who are covered by a universal, single-payer system.

MANY OF THE uninsured also receive medical care beyond basic preventive services. Based on the results of a Kaiser Foundation study authored by Jack Hadley and John Holahan, we found that the uninsured receive about half the dollar value of services as those covered by private insurance. They access care through a network of community health centers and free clinics, through some out-of-pocket expenditures as well as from free services provided by hospitals that are reimbursed through federal payments for uncompensated care.

The uninsured are a highly diverse group that varies considerably across the nation. Forty percent of the uninsured live in four states -- California, Texas, Florida and New York. Thirty percent of people ages 18-64 are uninsured in Texas compared to 11 percent in Minnesota.

The states with a high percentage of uninsured generally have a high percentage of immigrants. Thirty percent of the uninsured nationwide are immigrants, and most are not citizens.

The geographic and demographic diversity of the uninsured suggests that a prudent approach to aiding this group should involve a state-federal partnership that would take into account the size of the problem as well as the services they currently receive. A one-size-fits-all mandate makes little sense.

THERE ARE MANY reasons why policy-makers should not plunge into a new national health insurance plan, not the least of which is the troubled economy and the massive federal debt we have been accumulating.

The current woes facing Medicare should also signal a warning. Medicare is federally funded and operated, yet Medicare has not controlled its spending. This year, Medicare expenditures are expected to reach $500 billion, and the prognosis for the future fiscal status of the program is dire.

A plan for fixing Medicare should be No. 1 on the to-do list of federal health care reform. To add a potentially even more explosive plan for the rest of the population is sheer fiscal folly.