From my associate, Rob Graettinger, comes this amendment to his recent report in this space about the tax consequences of giving to Children's Hospital:

"As the man said, speak with authority, and if that fails, punt.

"It's my turn to punt. Last week, a few words escaped that forced me to eat crow rather than turkey on Thanksgiving.

"I had written that a taxpayer who donates $4,000 to Children's Hospital can expect a $4,000 reduction in his tax liability. Michael Lee Martin, a public accountant, wrote to disagree.

"'If your hypothetical taxpayer has an expected tax liability of $4,000 and decides to make a $4,000 gift to Children's Hospital, he will reduce his tax liability to $2,936. (A married couple filing a joint return with a taxable income of $22,796 would owe $4,000 in tax.) This is a tax savings of $1,064 . . . .

"'If our taxpayer makes the same gift next year, his tax liability drops from $3,596 to $2,628, for a tax savings of $968,' Martin says. The Internal Revenue Service concurs.

"And for those who don't itemize deductions, the new tax bill permits a married couple filing a joint return in tax year 1982 to deduct 25 percent of their first $100 in contributions, or $25. In 1984, they may deduct 25 percent of the first $300, or $75. In 1985, they may deduct 50 percent of all charitable contributions, and in 1986, 100 percent of all charitable contributions.

"The only stipulation is that the 1985 and 1986 deductions are limited to 50 percent of a taxpayer's gross income."