Business firms should use their "clout" to curb inflation in medical costs and seek reductions in the amount and kind of health care given, the U.S. Chamber of Commerce urged yesterday.

Business spent about $34.5 billion on employes' group health benefits last year, and paid for many services or hospital stays that were unnecessary or overpriced, chamber president Richard L. Lesher said in announcing a five-part proposal to solve the problem.

In an 18-month, $175,000 study, consultants found that employe health costs are rising at twice the rate of wages, and that they will double in five years and quadruple in 10 years.

"The country has gone about as far as it can in saving on administration" of health care costs, and "now we have to get to content and volume," said Dr. Paul Ellwood, who headed the study. He said physicians have mistakenly convinced people "that more health care equals better health care."

Ellwood said business, as the largest private investor in health care, has both the interest and the clout to intervene directly to cut costs. "We do have overwhelming evidence that it is possible to get the same results we're getting now with at least a one-third reduction in costs," he asserted.

The Ellwood group proposals include:

Physical fitness programs among employes, along with nutrition and health screening efforts.

Bargaining with insurance companies for better deals on policies, preventive services and out-patient treatment to save on hospital costs.

Business support for health maintenance organizations (HMOs), prepaid health care groups that have demonstrated they can cut costs through preventive treatment, less hospitalization and competition in some parts of the country.

Business community representatives on local and state health planning and regulatory bodies to monitor and preserve the interests of large firms.

By considering health care as an economic matter, rather than paying whatever price is asked for the "product," business can prevent the kind of federal regulation of the industry that President Carter has proposed, the chamber concluded.