It's been three weeks since the deadline for Americans to file their federal income taxes, and while the memory of April 15 is fresh, it's worth remembering that if everyone paid his or her fair share of taxes, the tax rates could be lower.

That's part of the thinking behind President Barack Obama's announcement this week that he wants to close some corporate tax loopholes and crack down on offshore tax havens used by some corporations and wealthy individuals to evade U.S. taxes.

News reports describe Obama's loophole-closing plan as his effort to make good on his oft-repeated campaign promise to "end tax breaks for companies that ship jobs overseas."

As good as the plan sounds, it's not simple — and it won't be easy, considering the lobbying clout of the companies likely to be affected.

Targeting corporate tax breaks for U.S.-based multinational corporations is expected to hit leading technology, pharmaceutical, financial and consumer goods companies. The New York Times reports that prominent names in these categories include Microsoft, Pfizer, Goldman Sachs, Johnson & Johnson, Merck and Proctor & Gamble.

In addition to being well-known corporate names, these companies employ some of the most powerful lobbyists in Washington, D.C.

Proposing to close loopholes involving foreign profits would mean higher taxes for most major U.S. corporations, including such giants as Google, General Electric, Hewlett-Packard and Intel.

The issue of tax credits for foreign taxes paid is complicated. The provision now under scrutiny was intended to protect U.S. corporations from being double-taxed, paying taxes in two countries. But the way it has worked out looks more like tax avoidance than tax equity.

Consider the Treasury Department report that in 2004, U.S. multinationals paid an effective tax rate of 2.3 percent on their foreign profits. According to the U.S. tax code, the corporate rate is 35 percent.

Another method of minimizing taxes involves offshore tax havens. The Times reported that almost 90 percent of the biggest 100 companies in the United States have subsidiaries in tax havens such as the Cayman Islands or the Bahamas. Citigroup has 427, Morgan Stanley has 273 and Proctor & Gamble has 83.

According to the Securities and Exchange Commission, a five-story building in the Cayman Islands is listed as the corporate headquarters for 18,857 companies.

Del Monte Fresh Produce, for instance, has its headquarters in Florida, but also has another address on Grand Cayman Island, for its filings with the SEC. The Grand Cayman address is credited with having allowed Del Monte to shift income and pay an effective corporate tax rate of just 3 percent in 2008.

Obama is right to go after these tax-dodging techniques, because for every dollar avoided through offshore tax havens or manipulation of tax loopholes, other companies and average American taxpayers have to make up the difference.

In addition to wanting to close tax loopholes, Obama also wants 800 new agents at the Internal Revenue Service to help crack down on tax avoidance and tax cheats.

Obama calls this week's plan to close loopholes a down payment on his longer-term goal of simplifying the tax code. And he doesn't have to look far to find reasons to simplify the income tax code and reduce cheating. Treasury Secretary Timothy Geithner, along with six other Obama Cabinet nominees, were revealed to have "tax issues," in which the White House vetting process found they had underpaid their taxes.

Obama's efforts to crack down on tax cheats and offshore tax havens is expected to have broad support in Congress. But his plan to close corporate tax loopholes and make it more expensive for U.S. companies to operate overseas will be met with resistance in Congress and intense lobbying by corporate interests, the very same interests that provide millions of dollars to re-election campaigns for members of Congress.

There is a paradox when it comes to corporate taxes. The U.S. reportedly has the highest corporate tax rate in the developed world, but U.S. companies, particularly the big multinationals, are among the least-taxed companies in the world.

The cracking down on offshore tax havens, tax loopholes and big corporations gaming the system will help boost tax revenues, but mostly it's about fairness. There is broad agreement that many big corporations are not paying their fair share of taxes. That needs to change, and Obama's plan is a step in the right direction.