It has been estimated that the "underground economy," that wide variety of legal-but-unreported business transactions, costs the government billions of dollars in lost tax revenue each year.

Of course, the dark side of the underground economy--all the illegal operations like drugs, prostitution and the various money crimes--doesn't contribute to the tax coffers either.

But the underlying problem there is different and not pertinent to this column. What is pertinent is a look at the new requirements the Congress built into the Tax Equity and Fiscal Responsibility Act of 1982 (TEFRA) in an attempt to reduce leakage of tax dollars from both inadvertent and intentional reporting omissions.

For many years income tax has been withheld from wages and salaries by employers, then forwarded to the IRS. Now TEFRA extends pay-as-you-go to retirement distributions and to interest and dividend payments. Beginning Jan. 1, income tax was to be withheld from both periodic and lump-sum payments from pension and profit-sharing plans, commercial annuities and individual retirement accounts.

There are provisions for relief. Many payers were not able to gear up to meet the Jan. 1 date. If that initial date caused "hardship," withholding may be delayed as late as July 1, 1983.

Withholding will not be required from payments expected to total less than $5,400 for the year ($450 a month). And any recipient can avoid withholding simply by filing a request for waiver with the payer.

On July 1 withholding is scheduled to start on most payments of interest and dividends. Unlike pensions, you can't avoid this withholding by requesting a waiver.

But there are exemptions. Withholding is not required on any account expected to earn $150 or less in interest (but not dividends) during the year. This annual minimum applies separately to each account; payers are not required to accumulate totals if a taxpayer has more than one account.

Single people whose federal income tax liability for 1982 didn't exceed $600 ($1,000 if 65 or older) are exempted from withholding on interest and dividends. For a married couple filing a joint return the waiver ceiling is $1,500 for youngsters, and $2,500 if either partner is at least 65 years old. Exemption is requested by filing Form W-6 with the payer.

Withholding will not be required on nontaxable distributions like interest in a municipal bond. And tax will not be withheld on earnings accumulating in an IRA or Keogh or an annuity; withholding will only apply to distributions from these tax-deferred plans.

Early in 1984 you will get a report of how much was withheld from pension payments and from interest and dividend earnings, much as you do now for tax withheld from wages. The 1983 tax forms will provide a place to take credit against your tax liability.

If you have been filing a quarterly estimated tax return because of pension payments or interest and dividends, you may want to adjust your estimates to take into account the new withholding.

In addition to the new withholding, several new information reports will be required from various sources. For example, if you get a state tax refund of $10 or more, your state will report it to the IRS.

(But you still need not report the refund as income unless you had deducted the tax paid on Schedule A in a prior year.)

Starting with 1983 transactions, brokers and mutual fund sponsors will have to report securities sales you make during the year, to be checked against capital gains you report on your tax return.

And for those who sell products from the home, firms like Avon and Amway will have to report to the IRS anyone who buys $5,000 or more of their products during the year.

The message is pretty clear: If you have income from any source, the IRS wants it reported on your tax return. And this should be welcome news to everyone (surely all my readers) who have been paying their fair share all along.