The Reagan administration has altered substantially the tax "expenditure" section of the budget to drop the major new business tax cut as a listed item and to stop showing whether the beneficiaries of tax breaks are corporations or individuals.

The tax expenditure budget is one of a series of special analyses the administration is required to produce under the Congressional Budget Act of 1974. At a time when Congress is looking with growing interest at the tax system as a source of revenue to lessen the deficit, it is a basic document describing revenue losses from special provisions in the tax code often described by reformers as "loopholes."

Neither the Congressional Budget Office nor the Joint Committee on Taxation plan to follow the lead of the administration when they develop their own versions of the tax expenditure estimates. The administration shifts angered tax reformers, one of whom, Robert S. McIntyre, director of Citizens for Tax Justice, said it amounted to "a major cover-up."

The tax expenditure budget shows revenue losses from a host of provisions in the tax code. The provision allowing homeowners to deduct interest on mortgage payments, for example, will result in $25.5 billion in losses in fiscal year 1983; special treatment of capital gains, $14.4 billion; the investment tax credit, $20.2 billion; and expensing of oil and gas exploration and development costs, $1.7 billion.

The changes in the special analysis were made at the apparent initiative of Norman B. Ture, Treasury undersecretary.

The analysis ends the practice of showing whether the beneficiaries of tax expenditures are individuals or corporations on the grounds that it is "consistent with the treatment of outlays spending , which are reported by function, not by whether the payee is a person or a corporation."