Presidential hopefuls Barack Obama and John McCain have clashed over the issue of tax reform.

Obama has pledged to introduce a windfall profit tax on oil companies and raise income tax for those earning over $250,000 a year if he wins the White House. McCain favors a lower corporate tax rate (from 35% to 25%) and suspension of fuel taxes during summer. Both seek tax cuts for the middle class.

“Investors should focus their minds around one uncomfortable fact,” says Martin Hutchinson in Money Morning. “Whether it’s Obama or Republican John McCain who wins the White House, expect some policy changes that won’t sit well with investors — or with the U.S. economy.”

Of all the anticipated changes, the most widely publicized is the expected introduction of a so-called “cap-and-trade” carbon-emissions-control system. Both Obama and McCain favor such a system and Congress is currently drafting legislation that is not expected to pass this year (while George W. Bush is still president), but to form a template for legislation from a Democrat-controlled Congress to be signed by either Obama or McCain in 2009.

The most economically efficient way to curb carbon emissions is by means of a carbon tax. Such a tax would penalize emissions by polluters at a flat rate per ton, and could be offset by reductions in other taxes - a decrease in the corporate tax rate, for example - thus neutralizing its overall economic effect.

Provided the tax was set at a moderate rate, it would provide incentives to shift from carbon-based fuels to other energy generation systems, while the market itself would determine which carbon uses would be discontinued and which were too expensive to change. It wouldn’t matter too much at what level the tax was initially set, since a moderate error in setting the level would produce only moderately suboptimal polluter behavior, as the incentives produced either a little too much clean-up and consequent economic damage, or not quite enough.

The carbon tax is unpopular with politicians, because of the word “tax.” From bitter experience, they have found that raising taxes leads to unpopularity and, ultimately, to electoral defeat. Even if other taxes are lowered, the squawks of the complaints and protest of the losers are always much louder than the contented purring of the winners. That explains their preference for a “cap-and-trade” emissions policy, under which politicians pretend to give something away, providing licenses to pollute, which can then be traded among users.

The main difference between the cap-and-trade schemes of McCain and Obama is this: McCain would allow the government to give out permits to polluters while Obama would auction off permits.

At first glance, McCain’s approach appears more pro-business, but consider this: If the government gives out the permits, it gets to choose which companies get what permits. That creates a huge new playing field for lobbyists and opens the door to all sorts of new opportunities for corruption, as polluters “compete” to gain the political favor of an emission permit allowance. Already in the draft Congressional legislation provision is being made for favored groups to be given special allowances of emission permits - essentially the same as the government giving them cash, as the permits will have value.

Under Obama’s proposal, however, the government will auction off the permits. That will ensure that their price is set by a market process, and that companies neither gain nor lose by their special access to legislators. It’s a much more honest process, and a much-better representation of the “free market.” And the extra revenue it generates can be returned to the taxpayers via tax reductions in other areas.

Indeed, the only disadvantage of Obama’s proposal compared to a carbon tax is that the government has to determine initially how much carbon should be emitted. That is a very difficult parameter to determine, and an error of 1%-2% in either direction can have a huge effect - as shown by the 2004-07 European Union emission permits, where too many were given out. As a result, the prices in the permit trading market dropped 98% in a couple of weeks, as companies discovered there were ample permits for all. A market with that degree of uncertainty is far more likely to result in corporate-finance game playing than in any serious reduction in emissions.

McCain’s proposal contains a number of additional potentially detrimental features. Under it, reducing emissions in emerging markets can satisfy emissions requirements. But as the European Union has discovered, one spin-off effect has been the creation of a thriving market in Chinese environmental-cleanup scams. Further complicating the scene is the fact that some industries would be partially exempted in order to allow for transitional difficulties - providing another fertile field for government meddling and corruption. Still, even with Obama’s proposal, a “cap-and-trade” system is likely to do significant economic damage, and given the fact that legislation would need to be drafted by Congress, the chance of huge economic distortions must be considerable.

A second area where both candidates essentially agree is that taxes will be higher. McCain obfuscates this, because he needs to preserve his relations with the Republican “base.” But he has made it very clear that fiscal discipline in terms of balancing the U.S. federal budget is his most important economic objective. And he favors further activity in the Middle East, a fact that’s likely to involve an expansion of defense spending. Since, even without a recession, the federal deficit in the years to September 2008 and 2009 will be close to $500 billion, McCain’s balance-budget objectives cannot be achieved without tax increases, both reversal of most of the 2001 and 2003 tax cuts and increases beyond that.

Obama has been more up-front about his desire to reverse the 2001 and 2003 tax cuts, and to impose Social Security contributions on incomes above $200,000. Since he also favored U.S. Rep. Charles B. Rangel’s bill, which increases income taxes on higher incomes, an Obama administration could potentially increase the top marginal rate of income taxes increase from 35% to 52%.

Obama also favors an increase in the capital gains tax rate from its current 15% to at least 20%. On the positive side of the budget, an Obama administration would presumably save money in the Middle East. And his health-care plan, which mandates coverage for children but not for adults, would presumably be somewhat cheaper than Hillary Clinton’s plan.

Nevertheless, tax increases are inevitable no matter who wins in November. And if Obama were to win those new levies might include a supercharged capital-gains tax and even dividend-tax increases - either of which could hammer U.S. stock prices.

A third area of agreement between the candidates is in greater regulation of the financial-services business. From the viewpoint of a retail investor, this may be a good thing: After all, who could object to fewer scams and rip-offs, or-less-egregiously overpaid investment bankers?