The Treasury Department released, a study yesterday concluding that large corporations pay much higher tax rates than is generally believed.

The study said that corporations with assets over $1 million paid between 39 percent and 46 percent of their income in taxes on the average in 1972, the year examined.

Large manufacturing concerns such, as auto companies, paid slightly less than 42 percent in taxes, Banks were the lowest of the groups surveyed, at slightly more than 19 percent. Treasury said the reason bank taxes were low is because banks have tax exempt income, such as bonds, and receive large tax breaks in the form of artificial bad debt reductions.

The report which Treasury described as "the most comprehensive set of such computations" it has prepared, appears to contradict the conclusions of several recent congressional studies.

Sen. Gaylord Nelson (D-Wis), chairman of the Senate Small Business Committee, has published studies by his staff that contend small businesses pay a far higher tax rate than larger ones.

And Rep. Charles A Vanik (D-Ohio), a member of the House Ways and Means Committee, annually issues a report claiming that dozens of big corporations pay extremely low effective tax rates - often less than 1 percent.

While not specifically citing the Vanik and Nelson studies, the Treasury report cautions that "much mischief may be done" by using the methods of computation the two congressmen employ, and branded their conclusions "misconceptions."

The document noted that in both cases, the lawmakers had reached their conclusions by comparing the taxes a firm pays the United States to its worldwide income, and by basing their calculations on techniques used in accounting.

By contrast the Treasury study compared worldwide taxes to worldwide income and used definitions and techniques that apply specifically to tax law. The Treasury said the other methods tend to distort the results.

The Treasury report showed these major conclusions:

Despite "common misconceptions," a compilation of actual tax returns filed by corporations shows big companies generally pay higher effective tax rates than do smaller businesses. The study showed that corporations with assets of less than $1 million paid taxes that amounted to between 20.6 percent and 34.3 percent of their income. Those over $1 million paid between 39.7 per cent and 46.2 percent.

Large manufacturing firms, such as auto companies, paid the highest effective tax rates among 19 major categories of industry, with an effective rate of 41.9 percent.

The industry with the lowest effective tax was banking, which paid 19.4 per cent of its income in taxes. Others included wholesale and retail trade, 38.8 percent; services, 31.6 percent and real estate, 28.9 percent. The petroleum and natural gas industries were listed as paying an effective tax rate of 59.4 percent. But Treasury tax experts said that was bloated by foreign royalties and other payments. The rate is closer to 24.7 percent.

The pattern remains the same whether the study compares U.S. taxes paid to U.S. income, or world-wide taxes to worldwide income. It is only when U.S. taxes are compared to worldwide income - erroneously, Treasury argues - that distortion results.

The group of corporations with assets of less than $1 million - generally classifed as smaller business - accounts for 75 percent of the firms subject to the U.S. corporate tax.

Nelson apparently misread the Treasury study as confirming what his earlier staff studies had shown and issued a press release, summarized in the Congressional Record, contending that it vindicated him.

But a tax expert familiar with both studies said Nelson apparently had looked only at a line is the report that comparied U.S. taxes paid to worldwide income - just what the Treasury warned against.

The source said Nelson "mislabeled" the Treasury figures.

The Treasury study was based on actual tax returns that corporations filed on 1972 earnings, after the firms claimed the investment tax credit. Officials said updating to include recent tax law changes would not alter the findings.