Publication of private financial data by appointees to the Carter administration has provided a rare glimpse into the earnings of corporate lawyers, a group that traditionally keeps such matters private.

The new data, released late last week, show that Cyrus R. Vance, the new Secretary of State, earned $250,444 last year from his senior partnership in the New York firm of Simpson, Thacher & Bartlett - a figure regarded as about average for a senior partner of major firm, according to numerous lawyers interviewed this week.

But Joseph A. Califano Jr., the new Secretary of Health, Education and Welfare, earned more than $555,000 as a senior partner of Williams, Connally & Califano in Washington. Lawyers in other firms expressed surprise - and in many cases admiration - about the size of Califano's earnings.

Califano earned more last year than Thomas A. Murphy, the chairman of General Motors, made in 1975, according to figures published by Business Week magazine. This year Murphy was the 15th highest-paid business executive in the United States.

Put another way, Califano earned more in a week than the average American worker made in a year in 1975.

Califano declined a discuss his income. The senior and founding partner of his old firm, Edward Bennett Williams, said, "whatever anyone is paid over here, he's worth it." Williams declined to discuss the apparent ability of his firm to generate much more income than other big law firms here and in New York.

"I regret deeply that they [the Carter administration] felt it was necessary to publish past earnings," Williams said. He thought a statement of net worth and private holdings would have satisfied the requirements of candor with the public.

Williams did say there was "no windfall explanation" for the size of Califano's earnings last year: "The facts are the facts."

Other lawyers speculated that Williams himself, as the senior partner of the firm, probably made more than Califano in 1976.

Major corporate law firms generally make money in two ways: billing clients at hourly rates ranging from about $40 to about $200, and collecting annual retainers from major clients.

Connolly prides itself on being more efficient than other law firms, accomplishing more for clients with less manpower.

A partner in another firm speculated that Williams & Connolly "is billing for accomplishments rather than hours." But Williams & Connolly is said to believe that "for a similar job the bill must be comparable" to what another firm would charge.

Several lawyers said a firm dominated by one or two strong personalities like Williams & Connolly was likely to earn bigger fees than a more staid corporate firm. They noted that Williams has won very big fees in successful courtroom actions, his specialty.

The firm declines to publicize the names of its clients, but public records indicate it has represented Coca-Cola; Pfizer, the drug manufacturer; The Washington Post; El Paso Natural Gas, and others. Williams himself has represented John B. Connally, the former Texas governor; Jimmy Hoffa, the former Teamsters union president and many other famous individuals.

The senior partner in one of the country's best known law firms said he was "surprised" at the published size of Califano's earnings. "It's amazing, really . . . It just hows that some people do it differently than others do."

The lawyer speculated that the gup between the shares of profits of senior and junior partners at Williams & Connolly is probably quite wide. Other firms try to keep that difference relatively narrow, he said.

There are many ways of dividing a firm's profits. Some relate a partner's income to the amount of business he brings in. Some pay senior partners the most simply because they are senior; others pay the highest amounts to the partners who are most active.

The profits of firms are generated largely by the young associates. They now start, in the biggest firms, at salaries of $20,000 a year and more, but their work brings in $40,000 or more per year from clients. Williams & Califano has 18 partners and about the same number of associates.