IRS Chairman Charles O. Rossotti began his tenure in 1997 with Congress thoroughly enraged at his agency; he ends it this week with the White House peeved at him. In between, observers say he took care of many of the management problems that had put the ire in IRS, and he left a warning that the Bush administration seems to have wished he hadn’t.

The conclusion in Washington and many other places five years ago was that the Internal Revenue Service was snoopy, abusive and mad with power. In response, a Republican Congress wanted to take oversight of the agency away from the Treasury Department and place it in the hands of an independent board. The Clinton administration resisted, offering instead a civilian-oversight board, which was formed in 1998. The management problems were reduced, though not eliminated, and those who wanted a major IRS overhaul went on to other battles.

But now they might return to the IRS, this time pursing not the collectors of revenue but the very creative people who cheat on their taxes while the agency says it lacks the resources of respond. According to the New York Times, the Bush administration stopped Mr. Rossotti from testifying before Congress about the extent and increasing number of tax cheats, especially among those who can afford expensive and sophisticated tax advice. What he would have told the House Ways and Means Committee is that the tax system is growing increasingly complex, funding to hire investigators is not keeping pace and the number of audits per 1,000 taxpayers has fallen precipitously in recent years.

Some members of Congress and some former IRS executives disagree in the degree of the problem described by Mr. Rossotti but most say the problem of tax cheats needs to be addressed. The administration has concluded that the agency will get enough of an increase that, when combined with simplifying the tax system and other reforms will allow for more audits. This winter is an ideal time for Congress to decide whether this is correct.

For instance, Mr. Rossotti said the IRS had identified 82,100 taxpayers who used offshore accounts to avoid paying taxes, but that the agency had resources to pursue only 17,000 of them. And because Congress has enacted 293 changes to tax law in the last five years, taxpayers have been able to take advantage of new taxpayer protections and partnership rules to misreport what they owe, knowing that the IRS probably will not check their returns.

There are a number of wild guesses what all this costs the Treasury Department in lost revenue and gets passed on to honest taxpayers. Congress should invite Mr. Rossetti back ask that question, ask other experts what the enforcement arm of the IRS needs to stay even or get ahead of the tax cheats and find ways to anticipate future areas of tax misconduct. Such hearings would be of particular interest to the voters who file on time and fully account for their incomes.