Just when the Internal Revenue Service is shouldering its heaviest workload at the April 15 deadline for filing income tax returns, the agency can also count on its heaviest load of criticism.

So perhaps a word of appreciation is in order out of simple fairness. Though the IRS' error rate is up when it comes to advising taxpayers, that's at least partly the fault of Congress, which made the tax laws more complicated when it was supposed to be simplifying them.Keep in mind, too, that even though the IRS handles a staggeringly heavy workload, it ordinarily does so smoothly and expeditiously.

Even so, it's hard to ignore a number of horror stories that have come to light lately involving blunders and abuses on the part of the IRS. The latest one involves a Texan whose check to the IRS was two cents smaller than it should have been. In response, the IRS sent him a bill for $400.31 in penalties evidently computed on the basis of the Texan's total tax obligation, not the shortfall.

Unhappily, this case is not unique; there are said to be literally thousands of others. The U.S. Chamber of Commerce recently categorized them along these lines:

* Taxpayers whose payroll tax deposits were mishandled by the IRS but still had levies placed against their bank accounts.

* Taxpayers who spent years and often thousands of dollars battling with the IRS over inaccurate computer-generated deficiency notes.

* Taxpayers who have simply paid erroneous tax bills, reasoning that it was easier to pay than to fight the system.

What can be done to correct such abuses? That's where the proposed new Omnibus Taxpayers' Bill of Rights Act, recently approved by the Senate Finance Committee, would come in. Basically, this measure would:

Allow taxpayers to collect damages and professional fees if the IRS acts unjustifiably or recklessly.

Require that tax-due notices be better explained.

Expand the authority of the tax court to help taxpayers.

Improve the IRS interview process by making it convenient for taxpayers.

Help to prevent needless disputes with the IRS by empowering a taxpayer ombudsman to issue "taxpayer assistance orders." These orders, as the U.S. Chamber of Commerce explains, would provide relief against unusual, unnecessary or irreparable loss due to abusive IRS actions. They also would be a quick and inexpensive way to resolve tax problems when traditional methods have failed.

The IRS should look on this plan not as an attack but as a way to help the agency improve its performance and its image. By all means, Congress should put the Taxpayers' Bill of Rights Act on the books.