The typical doctor in the United States earned more than $86,000 last year. Even so, his income failed to keep pace with inflation because, although he charged more, he had fewer patients, according to a new survey.

Medical Economics, a magazine for physicians that focuses on the business of medicine, found that private doctors' earnings in 1981 experienced the "smallest percentage gain in a decade" but concluded that "it apparently wasn't for want of trying." The magazine said doctors had experienced a "continuing decline in the number of patient visits."

Arthur Owens, the magazine's senior editor, attributed this downward trend to the recession and the tendency of patients "to avoid seeing their doctors any more than absolutely necessary." But, he added, the problem is "worsened by growing competition from a still expanding surplus of physicians."

Some of the magazine's findings:

Surveyed doctors' earnings after expenses rose 3 percent overall in 1981, as compared to 9 percent the year before and nearly 13 percent in 1979. This represented a "significant loss of purchasing power," said the magazine, given the 9 percent cost-of-living rise last year.

Doctors' fees went up nearly 12 percent last year. But during a representative work week, private practice physicians saw 6 percent fewer patients than a year earlier and 14 percent fewer than a comparable week in 1978.

In terms of median income, two out of five doctors netted $100,000 or more last year. Heading the list in terms of specialities are the neurosurgeons and orthopedic surgeons, who make about $136,000 and $135,000 respectively. The lowest earners were general practitioners, at about $64,000, and pediatricians, with just over $65,000 each. Median represents the point at which half of doctors make more and half less.

Over the past three years, the number of doctors engaged in active patient care has increased 11 percent.

The survey, which was based on a representative sample of about 6,000 doctors across the country, was publicized yesterday by Public Citizen's Congress Watch. The Ralph Nader-founded group is fighting the congressional push to exempt physicians and other professionals from the purview of the Federal Trade Commission.

Congress Watch said that the data helped explain why medical groups are attempting to "fix prices and restrict competition."

A spokesman for the American Medical Association, which is lobbying for passage of the FTC-exemption bill before the House, said yesterday that the organization has "long been an advocate of competition" but does not think the commission is "the appropriate regulator."