WASHINGTON -- Forget for a moment the controversy President Bush ignited when he suggested that the government should give religious groups a bigger role in solving America's social problems.

Consider something else he proposed the same day that has gotten much less attention, even though it would affect many more Americans: allowing everyone a tax break for charity.

At first glance, the idea seems so fair and logical that you have to wonder why it isn't being done already.

Under current law, only taxpayers who tend to be well off -- those who itemize deductions -- are permitted to claim deductions for money they donate to charity.

But the vast majority of taxpayers -- those who use a standard deduction calculated by the government -- are not allowed a break for charitable contributions.

That, Bush suggested, is not only unfair to the tens of millions of Americans who don't itemize their taxes. It also is silly, he suggested, because it discourages people from giving to charity.

Sure enough, the day after Bush's announcement, a national coalition of nonprofit groups and corporate philanthropy programs happily hailed his proposal and issued a study by a major accounting firm estimating that expanding the tax break would increase annual donations to charity by $14.6 billion.

"Of all the proposals the president has put forward, this one will have the greatest impact on stimulating new giving," said Sara E. Melindez, president of Independent Sector, which commissioned the study by PricewaterhouseCoopers.

So why would anyone oppose such a reasonable idea? Turns out there are some reasons worth weighing.

"It has a lot of political appeal, there's no doubt about that," says Sheldon S. Cohen, a former commissioner of the Internal Revenue Service. "But it's an idea which has been studied many, many times. And each time it comes up there are a number of problems. ... The problem with the Bush administration is it's coming in quick and it's not prepared and nobody's studied these problems."

The first problem, Cohen says, is that the fairness issue is misleading. People who don't itemize their taxes already get a pre-set standard deduction that assumes they are donating some money to charity, he says. In exchange for taking a pre-set deduction, taxpayers are spared the burden of proving they're eligible for particular deductions.

"The point of the standard deduction is to get people out of keeping records," says Cohen. "Everybody wants a simpler tax return and a simple tax system and then they keep adding these curlicues that make it complicated."

Second, he says, expanding the tax break would greatly increase cheating because tens of millions of Americans would start claiming donations that IRS agents would have a hard time verifying.

"These numbers are going to be so small that it will be impossible to check them," says Cohen. "You can't send a revenue agent to look for a $75 item. So you know that there will be cheating. Once it gets around that nobody ever looks at this deduction, everybody will claim it."

Of course, people who already itemize charitable contributions can also cheat. But Robert McIntyre, head of Citizens for Tax Justice, another group that opposes the expanded tax break, says the odds of cheating are lower among itemizers because they generally earn more money and claim multiple deductions. That means the IRS is more likely to watch them.

"It's a smaller subset of the population and there's more gold to be found there," says McIntyre. "So they're more likely to be audited."

Advocates of Bush's plan don't entirely dispute these arguments. They say, rather, that the arguments have some holes, and that overall, the benefits of encouraging charity outweigh the drawbacks. Melindez, for example, challenges the notion that cheating will become a much bigger problem if the tax break is expanded to non-itemizers.

"The people who do the most cheating are those who can hire accountants and lawyers to help them do it," she says.

And she says that while the standard deduction may have been designed decades ago with an assumption that most people give to charity, nobody can say whether it accurately reflects now what people actually give.

Leslie Lenkowsky, a professor of philanthropic studies and public policy at Indiana University, says charitable giving would increase under Bush's plan, but not as much as the Independent Sector study suggests. The best incentives for increasing donations to charity, he says, are a strong economy and a culture that encourages people to get involved with charities in their communities.

"People give to things that they're connected to," he says.

Lenkowsky, who advised the Bush administration on some aspects of its faith-based initiative, says he supports expanding the deduction but doesn't regard it "as a be-all or end-all." To allay the fears of critics, he suggests the tax deduction be expanded and the IRS do a random sample of returns afterward to see if fears of increased cheating are justified.

For his part, Cohen is not optimistic about what such a study would find. In the end, he says, politicians who support an expanded tax break are likely to find that everything has a cost.

"We are doomed to make hard choices," he says. "Politicians hate to make hard choices. So they make easy choices and they make a hard tax system."