The oil industry was by far the largest buyer of tax breaks under the leasing provisions of the 1981 Economic Recovery Tax Act, according to a study released yesterday by the Treasury.

The petroleum-refining industry bought $1.4 billion, or 20.6 percent, of a total of $6.78 billion in corporate tax benefits bought and sold in 1981, the Treasury found.

Except for Amoco, which was publicly very active in tax purchases, very few deals involving oil companies have been disclosed. Amoco reduced its federal tax liability by $159 million through tax purchases, according to the firm's 1981 annual report.

In purchasing the tax benefits, the oil industry came out ahead by $127.6 million, according to the report.

In contrast, the electrical and electronics industry, which would appear to include IBM, bought a smaller amount of tax breaks, but received a much higher return. The electronics and electrical industries bought tax benefits valued by the Treasury as $617.5 million and made a net gain on the deals of $168.9 million.

One of the biggest tax sale deals involved between $100 million and $200 million when Ford sold tax breaks to IBM. Industry sources generally reported that IBM made the deal on highly favorable terms.

On the other side of the coin, the largest seller of tax breaks was the railroad industry, which sold benefits valued at $748.6 million, closely followed by the lumber and paper industry, at $717.8 million worth of tax benefits.

In addition, the study found that third parties in lease deals such as lawyers, investment bankers and accountants received $108.8 million, or 1.3 percent of the value of the tax breaks. The companies selling the tax breaks got $5.7 billion, or 84.5 percent of the total value of the tax breaks, and the buyers got $964.6 million, or 14.2 percent.

These calculations have been disputed by the Joint Committee on Taxation, which, using a different method, found that 76 percent of the total revenue lost went to sellers of tax breaks (lessees), 22 percent went to buyers (lessors) and 2 percent went to middlemen.

The percentage going to the lessees is critical when attempting to determine the "efficiency" of the tax expenditure program. According to Treasury theory, the program has been 84 1/2 percent "efficient" while the Joint Committee contends it is 76 percent efficient. The percentages refer to the amount going to the "targets"--companies generally facing low profits and consequently without tax liability.

Neither finding of efficiency is as high, however, as the food stamp program, for example, which has an efficiency rating of 90 percent: 90 cents out of every dollar go to the people supposed to be served.

When viewed in terms of total dollar volume, the Treasury study found that the overwhelming majority of benefits--more than 85 percent--involved tax sales on equipment worth $10 million or more. In other words, these transactions involved big, not small, business.