The national medical bill rose by about an eighth last year to $322 billion, or 10.5 percent of gross national product, the highest such share in history, according to figures compiled by the Department of Health and Human Services.

The increase in medical costs was 12.5 percent, about twice the general rate of inflation. The new figures, still unpublished, mean that medical care now amounts to more than $1 out of every $10 Americans spend. The figures are certain to lend added urgency to administration and congressional efforts to curb health care costs to help hold down the federal budget and inflation.

The runaway medical inflation problem has now plagued four successive administrations of both parties. As recently as 1965, health care costs were only 6 percent of GNP, and were a relatively minor budget item.

Now health programs--particularly Medicare for the elderly and Medicaid for the poor, both instituted in the 1960s--make up more than a tenth of the budget, and without a tax increase or benefit cut the Medicare trust fund is thought almost sure to run dry in the next several years.

Last year was the first in which medical spending went over 10 percent of the GNP. In 1981, when the national medical bill was $286.6 billion, it was 9.8 percent.

Until now, most efforts to control medical care costs have involved increased federal regulation. In one of the most elaborate of these, the Carter administration proposed a hospital cost-containment program--in effect a moving cap on federal payments to hospitals each year. The hospital lobby smothered it in Congress.

The Reagan administration has now proposed a mixture of strategies, some increase in regulation but also some efforts to increase competition in the health care field on the theory that this will also help hold down costs.

At administration behest, Congress this year enacted a so-called prospective payment system for hospitals participating in Medicare, fixing the amount to be paid for each patient in advance. It goes into effect Oct. 1, but experts say it will not solve the problem.

The total of $322.4 billion health outlays in 1982 worked out to $1,365 per person, about $140 more than in 1981.

The figures showed that government spending--federal, state and local--totaled 42 cents out of every dollar of national spending for health, with three-quarters of that coming from the federal government, mainly for Medicare and Medicaid.

These two programs alone accounted for $83 billion in health spending with benefits for 48 million people, or a fifth of the U.S. population. Medicare hospital payments grew 18.8 percent in 1982.

Individuals paid nearly a third of the health costs out of their own pockets, and the remaining quarter came from private health insurance.

Of the total $322.4 billion outlays in 1982, $135.5 billion, or about two-fifths, went for hospital care.

Physicians received $62 billion.

Another $27.3 billion went for nursing home care, $22.4 billion for drugs and medical sundries, $19.5 billion for dental services, $14 billion for research and construction of medical facilities and $8.6 billion for government public health activities, with various amounts going to other types of services.

Underscoring the fact that health costs grew faster than the economy as a whole, the report said that employment and hours of work rose in the private sectors of the health industry, even as they fell in the private non-farm economy as a whole.

The unemployment rate for health workers and professionals was half that for the rest of the civilian economy, and compensation costs in private health establishments rose 15.1 percent, seven times the increase of the private non-farm payroll as a whole.

Increases in health costs were attributed to the aging of the population, proliferation of medical technology, slow productivity improvements and the labor-intensive nature of health care, consumer demand for more health services, tax breaks on health spending and cost-based reimbursement systems.