From time to time, we have discussed the potential for tax benefits associated with the use of a home computer for the management of personal investments. The Tax Reform Act of 1984 now provides specific guidance on the subject -- not particularly favorable guidance, either.

For computers put in service after June 18, 1984, you may not claim either the investment tax credit or depreciation expense for a computer purchased for the purpose of managing an investment portfolio.

The equipment must be used more than half the time for business purposes -- and "business purposes" does not include investments (unless you are in the investment business), even though your investments are intended to produce taxable income.

If you do meet the 50 percent test -- that is, the computer is used more than half the time in your business -- then you may also count its use for managing investments in determining what percentage of total use provides a tax deduction. But investment use alone does not qualify the computer for the ITC or depreciation deduction.

Regardless of whether the computer qualifies for a deduction, however, you may claim, as investment expense on Schedule A, the cost of special investment software as well as associated expenses, such as connect charges and fees for the Dow-Jones retrieval service.

Beginning next Jan. 1, you will be required to maintain detailed time-of-use records to support the percentage of computer use dedicated to business and investment purposes. Although not required now, I suggest you start keeping such records now to get in the habit.

The new law also puts a cap on the amount that may be claimed for both the investment tax credit and for depreciation on automobilies used for business. The new rules are aimed at luxury cars, limiting the ITC to a $1,000 ceiling and allowing a maximum of $16,000 to be written off in depreciation during the first three years.

For the past few weeks, we have reviewed the most important provisions of the Tax Reform Act of 1984 affecting individuals. This has not been anything like a complete review; there are other changes for the individual taxpayer and a number of new rules for business.

Those provisions not discussed yet may be covered in this column as readers raise questions about individual changes. At any rate, all of the changes will be reflected in more detail in the annual tax guide, which is expected to appear in Washington Business some time next February.

Question: Having just paid my June 15 estimated income tax, I'm once again upset with the provision that provides only two months to set aside this second "quarterly" payment. Does this skewed date relate back to the time when our taxes were due March 15? Or is it a result of the Treasury's need for cash in June? Just what is the rationale for having only two months for estimated tax payment No. 2? I'm always in a financial bind each June 15 because of having only two months to set aside the funds from my pension and Social Security.

Answer: I could find no one who could give me a firm answer to this question. Your guess about the origin of the date sounds reasonable, since June 15 is three months after that March 15 date.

Why wasn't the date moved to July 15 when the April 15 reporting date went into effect in 1955 (for the 1954 tax year)? Well, at that time the fiscal year ended on June 30. Slipping the payment date for the second installment of estimated tax would have moved a pretty big chunk of government income from one fiscal year to the next, and would have generated a substantial one-time increase in the federal deficit.

When the end of the fiscal year was moved from June 30 to Sept. 30, the June 15 date could have been shifted to July 15. But then the third payment date would have raised similar problems; keeping it at September 15 would have meant a two-month interval, but slipping it to October 15 would have meant delaying the income to the next fiscal year.

To ease your bind a little, I can suggest that you pull the necessary funds out of the "free" month provided by the four-month space between the Sept. 15 and and Jan. 15 payments and stash it away someplace in anticipation of needing it the following June 15.