More than a few taxpayers are grumbling, with the April 17 deadline for filing federal income taxes just one month away. Filling out a tax return can be a chore, and sending a check to the U.S. Treasury is generally not a pleasant experience.

But the normal irritation associated with the arrival of tax season is worse this year after an Internal Revenue Servicereport released in February revealed that an estimated $345 billion in federal taxes remained uncollected for the 2001 tax year. That amount of uncollected revenue is staggering — and, if collected, would be nearly enough to erase the budget deficit.

It is one thing to understand that the federal budget could be balanced if all taxes owed were paid. But a greater frustration for the average, honest taxpayer is the knowledge that that level of tax cheating or tax avoidance occurs and is tolerated. Worse still is the fact that taxes are higher for honest taxpayers because of those citizens who aren't honest taxpayers.

The IRSsays it expects to collect about $55 billion of the $345 billion owed from 2001. That's not nearly enough. Tax collection should be more aggressive, and Congress should ensure that those efforts are funded adequately.

Breaking down the report, the IRS points to a problem with small businesses not reporting income. Businesses most likely to cheat the Treasury include sole proprietors, independent contractors and the self-employed. Those, and all other tax cheats, should be pursued and made to pay their fair share.

But beyond the problems of cheating by failing to report, or under-reporting taxable income, the IRSacknowleges that the complexity of the tax code also is a problem.

Over decades, the federal tax code, with rules and rulings, has grown to over 60,000 pages. This complexity leads some taxpayers to pay more than they owe, and others to pay less than they owe.

It must be remembered that the IRS is not to blame for the complex code — that's Congress' doing. And lawmakers of both parties have used tweaking and adjusting the tax code as a powerful favor-granting tool that benefits both special interests and campaign contributors.

The complexity issue not only causes confusion among taxpayers and hides favor-granting by lawmakers, it also results in the expenditure of huge amounts of time and money. It has been estimated that more than $250 billion and 6 billion hours are spent annually complying with the overly complex tax code. That's time and money that could be spent more productively.

Based on the incredible amount of uncollected taxes, the growing failure by millions of U.S. citizens to pay what is owed and the unnecessary complexity of the federal tax code, the argument for a national sales tax gains strength. The main appeal of a national sales tax is that tax avoidance is nearly impossible — if you buy something, you pay tax to the U.S. Treasury.

A national sales tax would mean that people in cash businesses cannot avoid taxes by under-reporting their income. They would pay federal taxes when making purchases.

Americans should not tolerate the status quo on uncollected taxes. All citizens should be compelled to pay what they legally owe.

The current system depends on largely voluntary compliance. But the more common that such cheating becomes, the likely result is a breakdown of the whole system. As the level of cheating or non-compliance grows, honest taxpayers are made to feel like fools for following the rules.

In the short term, the current system can only survive with aggressive IRSefforts to catch willful tax cheats and force them to pay — along with stiff penalties and interest. Reducing the complexity of the tax code, though politically difficult, would help in reducing unintentional underpayment.

Over the long run, serious debate should examine a shift from the hopelessly complex tax code full of loopholes to a national sales tax that hits everyone when they make a purchase. Under such a system, non-compliance is not an option.

If the IRS report on 2001 uncollected taxes is accurate and representative, then close to $2 trillion in taxes due have gone unpaid in the years since.

Congress should act aggressively and quickly to crack down on illegal tax avoidance. To do anything less suggests that tax cheating is acceptable, and once that attitude gains a foothold, the entire system is in danger of collapse.