More than 90 million taxpayers are about to get some unexpected greetings from the Internal Revenue Service -- a reminder that the new tax law is like nothing they've ever seen.

The IRS announced yesterday it is spending $7.6 million to mail a brief, six-sided brochure in hopes of reducing the confusion when taxpayers begin filing their returns early next year. Those returns will be the first reflecting the new tax law for most people.

By the end of the month the brochures should be in the hands of most people who filed returns for 1986, according to Ed Pecorella, assistant commissioner in charge of taxpayer service.

The mass mailing, largest ever undertaken by the IRS, is the latest step in a campaign by the agency to get people thinking about their 1987 returns long before the April 15 filing deadline.

"Our brochure is a taxpayer alert -- an attempt to drive home the importance of readiness ... to discourage taxpayers from thinking they can put aside the new tax law and conduct tax business as usual," Pecorella told a news conference.

The brochure includes a tear-out coupon that taxpayers may mail to request a copy of Publication 920, a 55-page explanation of highlights of the 1986 tax law. The publication includes a side-by-side comparison of the old and new laws.

The brochure mentions some of those changes: lower tax rates, higher personal exemptions and standard deductions, elimination or reduction of several itemized deductions and new rules that may require students and some other part-time workers to file returns for the first time.

"We have people {IRS workers} around the country who are training on the new tax law earlier than ever before," Pecorella said. As a result, he added, the agency expects the taxpayer-service representatives who take questions from the public to be better equipped to answer.

The IRS will have nearly 7,000 employes working in taxpayer service, up 1,300 from this year. But don't wait too long to call them, Pecorella advised.

"The simple fact is {that} our ability to deliver quality customer service won't improve with time, so start thinking about taxes earlier than ever before," he said. "Figure out how these changes will affect you personally. And once your tax package {of forms} arrives {in December}, don't stuff it in a drawer."

The IRS is prepared to help in another way.

By calling the Tele-Tax number listed under IRS in the U.S. government section of the telephone book, you may listen to a tape recording, identified as No. 315, that highlights some of the major tax changes.

Ask for tape No. 326 and you get a listing of other tapes on specific topics, ranging from the new requirement that children 5 or older have Social Security numbers, to changes affecting individual retirement accounts.