President Reagan turned down $50,000 for redecorating the White House which Congress had authorized and accepted private donations to do the same thing. Fine - it saved the taxpayers that amount, said most readers. Not at all said tax authorities - these donations may be deducted in whole or part from the donors' income tax returns. They are part of what are called ''tax expenditures, '' tax deductibles, or simply ''loopholes.'' In the Treasury deficits facing the country they deserve another look. They are the fastest growing part of the federal budget; a relatively hidden form of subsidy. Many are for estimable purposes, some have been pried loose by powerful private interests. One study estimates that they amount to $266 billion.
Budget director David Stockman brought loopholes to the attention of President Reagan in the anxious days when he saw a crisis building in the budget (but was not saying so to Congress). At least that's the record in the recent article in the Atlantic. His appeal to Mr. Reagan against loopholes was unsuccessful. The magazine article included such targets as ''elimination of the oil-depletion allowance, an attack on tax-exempt industrial-development bonds, user fees for owners of private airplanes and barges; a potential ceiling on home mortgage deductions . . . some defense reductions and other items, 10 in all: total additional savings: somewhere in the neighborhood of $20 billions.'' He observed: ''Do you realize the greed that came to the forefront? The hogs were really feeding.''
Sen. Pete Domenici (R) of N.M., chairman of the Senate Budget committee, also complained of a tax loophole on CBS's Face the Nation, Nov. 29: ''There is one where we find a billion and a half dollars where pharmaceutical companies get to build buildings in Puerto Rico, and they get a huge tax break that is a carryover from a 1930 law that was aimed at helping the Philippine Islands.'' He added, ''In tax loophole expenditures it is costing $48,000 per employee. That just has to be looked into.''
The public interest group Common Cause (itself tax exempt) issued a 32-page study called ''The Untouchables'' last September, dealing with tax loopholes. It agreed that many tax expenditures ''meet legitimate public policy objectives.'' But some, it charged, are ''out of date, inequitable, and inefficient.'' It calls them ''Gimme Shelters'' whose sponsors ''make a quick congressional shopping trip to the tax-writing committees'' and try to grab a subsidy. Here's an example which disturbs Common Cause: ''The tax system will continue to support advertising for tobacco products while the federal government reduces by one-third its efforts to warn Americans about the health risks of smoking.''
These tax benefits are often directed at specific goals. Congress, for example, has nearly wiped out the estate tax, by raising the value of an estate that can be passed to an heir tax-free, from $175,625 to $600,000. Obviously that's a benefit to the affluent rather than the poor. By one estimate it leaves only 0.3 percent of all estates subject to federal tax. Congress was also generous to gift-givers: total cost of new estate and gift tax largesse may come to $204 million in FY 1982, and $5.6 billion in FY 1986.
Tax benefits ought to be reexamined periodically says Sen. Nancy Kassenbaum (R) of Kansas; she has legislation for limiting, coordinating, and revising the programs. One man's tax break is another man's higher tax burden. Sometimes it has an upside down effect on rich and poor. A $100 tax deduction equals a $70 saving for a taxpayer in the 70 percent top tax bracket (to be reduced to 50 percent on Jan. 1, 1982) but only a $14 subsidy for a taxpayer in the lowest tax bracket. For example, the Congressional Budget Office guesses that the 2 percent of the taxpayers who have incomes that exceed $50,000, receive 22 percent of all the benefits from deducting interest paid on consumer loans.
MIT economist Lester C. Thurow wrote last month of the new tax cuts: ''They were so large that they for all practical purposes have eliminated the American corporate income tax.''
The Joint Committee on Taxation thinks that ''tax expenditures'' will be costing the Treasury $553 billion by FY 1986. Administration tax advisers say the Treasury deficit will have reached $200 billion by FY 1984 unless something is done about it. What gives?