Senator Obama is unveiling a tax plan in Washington today, which he says will give “a break” to middle-class Americans, seniors, and homeowners facing anxiety and uncertainty.

He withheld details about the proposals during a speech calling for more transparency and openness on Wall Street yesterday, but he said they would modernize and simplify the tax code, giving relief to more Americans.

“For far too long, our tax code has been so riddled with special interest loopholes and giveaways that it’s shifted the tax burden to small businesses and middle-class Americans,” he said, speaking to business executives at the Nasdaq market in Times Square. “At a time when most Americans are facing stagnant wages and rising costs, that is not fair, and it doesn’t benefit our economy.”

Mr. Obama has said he would let President Bush’s tax cut for Americans making more than $250,000 a year expire in 2010 and use the revenues to pay for his health care plan. Mr. Obama talked tough to the Wall Street crowd, challenging the executives to acknowledge that for millions of Americans the benefits of free trade have been outweighed by its burdens.

“I think we must admit that those who have benefited from the new global marketplace — and that includes almost everyone in this room — have not always concerned themselves with the losers in this new economy,” he said.

Using the subprime mortgage meltdown to illustrate the economic devastation wrought on some Americans, Mr. Obama proposed establishing a federal definition of mortgage fraud and creating a metric by which consumers could compare mortgage plans more easily.

He said government must also investigate the relationship between rating agencies and their clients, and he proposed creating a credit card rating system to help consumers understand the level of risk they face when opening a new account.

He cautioned against a business world where “the quick kill is prized without regard to long-term consequences for the financial system and the economy,” adding that while such behavior might “benefit the few who push the envelope as far as it will go, it doesn’t benefit America, and it doesn’t benefit the market.”