Among the many grand traditions of this cheery holiday season is the annual package from your friendly regional director of the Internal Revenue Service. The IRS has begun sending out 1981 federal income tax returns; 88.7 million of us will receive them in the mail this week or next. (If you don't get one in the mail, you still have to pay. You can pick up forms and instructions at banks, post offices and federal offices.)

About 60 percent of the nation's households will get a package containing the standard form, 1040, plus instructions and tax schedules. The rest will receive the short form, 1040A, which can be used by people with taxable income up to $50,000 (and no itemized deductions). This huge burst of mail will run the IRS's postage bill for this week to $7.7 million. But then, the government expects to take in more than $300 billion through the individual income tax in fiscal 1982.

Despite all the changes in the big tax cut law passed last summer, Form 1040 still looks pretty much the same. There's a new line reflecting the new exclusion for interest income, and another new line for reporting certain pension information. Otherwise, the big changes are reflected in the small print of the tax rate schedules.