Most tax expenditures or loopholes -- are regressive, according to a study released yesterday by the Joint Economic Committee. Of $156.6 billion in lost revenues, just over $112 billion, or 71 percent, was found to help upper-income persons.

The single most regressive federal tax break, one that benefits from the political muscle of state and local governments and the banking lobby, is the provision allowing anyone who holds a bond to exclude from taxable income the interest received from the bond.

Other major tax breaks that provide the overwhelming proportion of benefits to the affluent are capital gains tax rates, the charity deduction, the deductibility of non-business state and local taxes, and the investment tax credit.

Only 5 percent of tax expenditures, costing the government $7.7 billion, could be described as roughly proportional. These include the deduction for medical expenses and a special exemption for the elderly.

Just under a quarter of the tax breaks, costing $36.6 billion, are progressive. These include the exclusions for Social Security benefits and for unemployment payments, along with the earned income credit, which is specifically directed toward the working poor.

"Some large tax expenditures have exceedingly regressive impacts on our tax system," said Rep. Henry S. Reuss (D-Wis.), chairman of the committee.

The study is based on a Treasury Department report that showed how the benefits of 33 tax expenditures are distributed to different income classes.

This year, Congress enacted legislation raising taxes by $98 billion over three years largely by closing breaks directed toward business. Next year, if Congress decides to increase taxes again, it is likely to give serious consideration to the elimination of expenditures benefitting individuals.

A tax expenditure, according to the Congressional Budget Act, is a loss of revenue created by provisions in the code allowing "special exclusion, exemption or deduction from gross [taxable] income" or "a special credit, a preferential rate of tax, or a deferral of tax liability."

The 33 expenditures in the study resulted in an estimated revenue loss of $156.6 billion this year.

The Treasury was unable to provide data on 19 other expenditures resulting in revenue losses of $15.9 billion. Among these, many of which tend to benefit affluent taxpayers, were percentage depletion, elimination of capital gains on estates, and exclusion of interest on life insurance savings.

In calculating the "regressivity" of each tax expenditure, the committee determined the percentage of the break going to taxpayers with adjusted gross incomes in excess of $50,000.

These persons, Reuss said, make up "only 4.4 percent of all taxpayers, receive 19 percent of total adjusted gross income, and account for 32.9 percent of taxes after credits."

The study also found:

* 94.1 percent of the exclusion of interest on state and local bonds, which costs the Treasury $4.6 billion, goes to the 4.4 percent of taxpayers with incomes above $50,000. Put another way, $4.4 billion goes to taypayers making more than $50,000; $265 million, or 5.6 percent, goes to taxpayers making from $20,000 to $50,000; and $16 million, or 0.3 percent, goes to those making less than $20,000.

* Of the $13.2 billion in lost revenues resulting from the lower rate on capital gains income -- the profits from assets held over one year, excluding homes -- 63.5 percent, or $8.4 billion, goes to those making more than $50,000.

* Similarly, the charity deduction benefits the affluent. Of the $8.8 billion in lost revenue resulting from the provision, 55.3 percent, or $4.9 billion, went to taxpayers with incomes above $50,000.

Other major tax expenditures, their cost to the government, and the percentage going to persons making in excess of $50,000:

Deductibility of non-business state and local taxes, other than property taxes, $17.8 billion, 47.3 percent to high-income persons; the investment tax credit, $3.4 billion, 46.9 percent; deductibility of property tax on owner-occupied homes, $8.7 billion, 38.2 percent; the consumer interest deduction, $8.2 billion, 32 percent; deduction for mortgage interest, $19.6 billion, 30 percent; exclusion for pension contributions and earnings, $24.3 billion, 26 percent; and deductibility of medical expenses, $3.4 billion, 24 percent.