Health care costs have risen so fast in the last two years that many American corporations now spend an amount equal to one-fourth of their net earnings to provide medical coverage for their employees, according to a nationwide benefits survey released yesterday.

The survey by Foster Higgins & Co. of New York, a major benefits consulting firm, shows the average company spent 21.6 percent more last year to provide doctor and hospital care to their employees than the year before. Over the past two years, the cost to employers has risen 46.3 percent.

The annual survey of 1,955 employers is one of the largest of its kind covering primarily large and medium-sized corporations. On average, companies spent $3,161 per employee to cover their medical costs last year, up from $2,600 per employee in 1989, according to the survey.

Health care costs for the 32 Washington-area firms included in the survey rose an average of 23.6 percent, with the cost of benefits rising from $2,846 per employee in 1989 to $3,519 in 1990. The area firms were not identified.

John Erb, who directed the study, said an increase in large catastrophic claims and increased use of medical care as a result of the current recession were major factors in the sharp rise in medical costs last year. The increased costs due to the recession, he said, tend to come from people who, fearing they might soon lose their jobs, had elective surgery.

A third factor, Erb said, was a continuing increase in the use of mental health and substance abuse benefits.

Erb said advanced medical technology has dramatically increased the amount of some claims. "We've seen companies with a $2 million claim for one person. That wasn't possible 10 years ago because we didn't have the {expensive} technology," Erb said.

To curb rising mental health costs, Erb said, many employers were simply cutting back on coverage, particularly in-patient care.

The latest survey results may serve to accelerate the shift by many employers toward so-called managed health care programs in which companies limit the medical care of their employees to doctors and hospitals that agree to provide care for a set price.

"Controlling medical expenses through traditional health plans has become a losing proposition," Erb said. "Employers who have put off addressing the health cost crisis will now be forced to consider a managed care approach."

In making the switch from traditional care to managed care, many companies have offered employees a choice of paying more for the right to choose their own doctor. But Erb predicted that companies will increasingly stop offering traditional care altogether.

Some major corporations such as Chrysler Corp. and American Airlines Inc. have been calling for Congress to enact an employer-based national health insurance program, arguing that it is the only way to combat health care inflation. These corporations have joined with organized labor and other groups for what they hope will be a major lobbying effort this session of Congress.

Many companies argue that the current focus on managed health care is the last stand before national health insurance. "Managed care is sort of our last hope," said Erb. "We haven't seen any innovative things on the horizon."

Don Moran of Lewin and Associates, a Washington-based consulting firm to medical insurers, said the health care costs of smaller companies, which often do not offer the same level of medical benefits as the larger companies, may actually begin to turn down a bit in the coming year. But he said the rate structure for smaller firms was cyclical and predicted rates would shoot up again in a year or two.