Update: In the July 14th column a reader asked about the president's tax credit for energy conservation measures I said then that it was not forgotton -- that the credit would probably be a part of the tax bill when it was finally passed .

Well, the Engergy Tax Act of 1978 -- companion measure to the Revenue Act of 1978 -- does include what is called the "Residential Energy Credit." There are actually two different credits authorized:

A credit of 15 percent of up to $2,000 expended for various "energy conservation" improvements, such as insulation, storm doors and windows, etc.

A credit of 30 percent of the first $2,000 plus 20 percent of the next $8,000 spent on "renewable energy source equipment" like a solar energy or geothermal heating or hot water system.

There are a number of qualifications attached to the credit. Look for a more detailed explanation in the annual income tax series, to appear in this section around mid-February.

Question: I recently bought some Treasury bills. They won't mature until some time next year. When do I report the interest income ?

Answer: The general rule for most taxpayers (who are on a cash rather than accrual basis) is that interest income is reported in the year it is received or otherwise made available to you.

Treasury bills are no exception. These short-term obligations of the U.S. government are bought at a discount and redeemed at face value. The difference between the two amounts is interest income.

But it is not income until you redeem the bills. In your case, the interest should be reported on your 1979 tax return. (Incidentally, I'm sure you know that while the interest is subject to federal income tax it is exempt from state income tax).

Q: Considering the new tax law, is there anything I can do now to save on my income tax ?

A: Year-end tax strategy must be an individual thing, developed in the context of a particular taxpayer's situation.

But I can offer some generalizations. With wider tax brackets, lower tax rates, and an increase in the personal exemption all set for Jan. 1, 1979, most people are going to find their tax bills a little lower next year.

So if you expect your family and financial situation to be approximately the same in 1979 as in 1978, you should defer income if possible) from December to January, when it will be taxed at a lower rate.

On the other hand, if you itemize, a deduction taken in 1978 will be worth more in tax savings than the same deduction taken next year. So if you have the funds available, pay your fourth quarter state tax estimate in December instead of waiting until the Jan. 15 due date.

And in December send any contribution to your church or other charity that you were planning for early 1979. You can wait until the end of the month; if you put the check in the mail by Dec. 31, it qualifies as a 1978 deduction even if it isn't received and cashed until some time in 1979.

Because the zero bracket amounts (ZBA) go up on Jan. 1, you might want to take a look at "alternating" deductions. That is, you itemize deductions one year, then use the ZBA -- the old standard deduction -- the next.

Then you adjust your payments for deductible items -- taxes, medical expenses (above the minimum exclusion), contributions, etc. -- to shift as much as possible from the ZBA year to the year you itemize.

If your normal total of itemized deductions hovers right around the ZBA, you can come up with a surprisingly large tax savings by using this technique.