The deadline for contributions to a Keogh plan was stated incorrectly in Sunday's Washington Post. The correct date for 1977 returns is April 17, 1978 or the date of an extension for filing, if one is granted. The maximum of 15 per cent of 1977 income, or $7,500, still applies but excess contributions made after Jan. 1, 1978 can be deducted from 1978 tax returns. It also was stated incorrectly that an employee who is not yet vested can set up an Individual Retirement Account. The employee may do so only if he or she has opted with the employer's permission not to participate in a company plan.

Question: I have been putting $1,500 a year into an IRA since the program started. I understand that the ceiling has been raised to $1,750 if I start an IRA for my wife. Does this mean I can put $1,500 into my IRA and the other $250 into hers?

ANSWER: Sorry - it doesn't work that way. The Tax Reform Act of 1976 did increase the maximum and authorize a separate IRA for the non-working spouse of an eligible worker, starting in 1977. But you must split the total payment equally between the two accounts.

Thus if 15 per cent of your annual wages is at least $1,750, the maximum you can deposit into each account in $875. If you want to put only $500 into your wife's IRA, then onlyv$500 in your account will qualify for the deduction on your tax return.

Of course if both you and your wife are employed and you are eligible individually for an IRA, then you can each deposit up to 15 percent of your separate earnings (not in excess of the $1,500 ceiling).

Incidentally, you can't use a "joint" IRA - you must have a separate account for each of you, or a single IRA with individual sub-accounts; and each owner has an immediate vested interest in his or her own account.

Q: My wife and I are doing research for a future jointly written book. The research entails considerable travel and other expenses. We expect no income from the book until publication, in perhaps two or three years. Can the expenses be deducted from our income from other sources (like taxable retirement pay) in the year in which they are incurred?

A: This is a grey area, with no firm rule available, according to the IRS. The service suggests that you "capitalize" these expenses. That is, don't deduct them as they occur, but rather accumulate them and charge them against the income from the book when it is published.

If you never get that far, then you may deduct all the accumulated expenses in the year the project is abandoned.

This is a conservative position. I think it is at least as appropriate to deduct your research and writing expenses in the year they are paid. I believe this method is in line with a basic IRS principle: Any reasonable accouting technique not specifically outlawed is permitted so long as you are consistent and the method selected does not result in a material distortion of income.

Use Schedule C, showing your deductible expenses and "zero" income. And attach Form 5213 to postpone application of the IRS "five-year test" (profit in two of five years) used to separate a bona fide business from a hobby.

Q: My mother died in 1953, leaving only a home in West Virginia worth about $15,000 at the time. There were three heirs - one of whom has always lived in the house - and no settlement was ever made. We now plan to sell the house, which has appreciated in value to $150,000. How will my tax liability be determined on my share of the proceeds?

A: Since your mother left only the $150,000 house when she died, there should have been no estate tax due. Here's how to figure your income tax liability now on the sale of the house.:

Start with the fair market value of the property at the time of your mother's death - $15,000, according to your letter. Add to that "cost" basis the cost of all capital improvements (permanent additions that increased the value of the property, such as storm windows, a driveway or patio, or an extra bathroom).

Then substract any reduction in the basis of the property because of a casualty loss like a fire or storm damage.

Now subtract the net result - the tax basis of the property - from the net proceeds from the sale (after deducting selling expenses). The result is a long-term capital gain; you - and the other two heirs - should cach report one-third of that gain on Schedule D of your individual tax returns.

Caution to other readers: The rules for figuring the tax basis on inherited property were changed by the Tax Reform Act of 1976. If you inherit property from a person who died (or will die) after Dec. 31, 1976, see the IRS or your tax accountant for the new regulations.