An article in yesterday's Business section said the Internal Revenue Service had made no attempt to notify self-employed taxpayers with Keogh retirement plans that they were required to file a new form with the IRS by July 31. In mid-1984, the IRS sent 650,000 notices to Keogh holders telling them about the new requirement. However, those notices went only to holders of one type of Keogh, who already were required to file a different form. Taxpayers who started Keogh plans after that, or were not previously required to file, were not notified.

The Internal Revenue Service said yesterday it "probably" will be lenient on self-employed taxpayers who are late in filing new forms with information about their "Keogh" retirement plans but will not automatically waive the $25-per-day penalty for non-filers. The fee will be charged starting today.

Those who couldn't get copies of the form or of the form requesting a filing extension or who had trouble filling out the five-page form should attach a letter explaining the reason for filing late, spokesman Steve Pyrek said.

"We will look at each case separately," Pyrek said.

Every self-employed person who has an individual tax-deferred retirement plan, including those who never have filed such a form before, must file Form 5500-C.

The IRS said yesterday that receiving an extension of the July 31 deadline will be more difficult than first thought, however, because the service will review each request. Officials had said Tuesday the extension would be automatic if the form was postmarked by July 31.

Taxpayers who asked to file 1984 tax forms late get an automatic extension on the Keogh form.

Filling out Form 5500-C can be a little difficult, however. It has at least three errors. In one place, the form asks for the taxpayer's assets, to be copied from another line. That line, however, is where the taxpayer was to state liabilities. In another portion of the form, questions 21(a) and 21(b) are identical. Elsewhere, a reference to another line is incorrect.

That's if you can get Form 5500-C. The IRS office in Wheaton ran out of the forms, and the instructions on how to file them, for at least some time yesterday. Callers to The Post also said Wheaton employes posted a large sign saying, "No Help on 5500 Forms." No difficulties were reported in other area offices.

The forms have not been required before for many holders of Keogh plans. The 1982 tax law extended the requirement to taxpayers with the simplest type of plan, and the IRS notified accountants and other tax professionals of the change. It did not, however, directly notify the affected taxpayers.

Taxpayers can breathe a sigh of relief once all this is over, however. The form only needs to be filed once every three years. A shorter form must be filed in the off-years.