Both admire, even adore, the United States, they say, for its entrepreneurial drive, innovative spirit and, not least, its academic excellence: the two met while re-searchers in Cambridge, Mass. But both also express bewilderment over the current conversation about whether the wealthy, who have taken most of America’s income gains over the last 30 years, should be paying higher taxes.

“The United States is getting accustomed to a completely crazy level of inequality,” Mr. Piketty said, with a degree of wonder. “People say that reducing inequality is radical. I think that tolerating the level of inequality the United States tolerates is radical.”

As much as Mr. Piketty’s and Mr. Saez’s work has informed the national debate over earnings and fairness, their proposed corrective remains far outside the bounds of polite political conversation: much, much higher top marginal tax rates on the rich, up to 50 percent, or 70 percent or even 90 percent, from the current top rate of 35 percent.

The two economists argue that even Democrats’ boldest plan to increase taxes on the wealthy — the Buffett Rule, a 30 percent minimum tax on earnings over $1 million — would do little to reverse the rich’s gains. Many of the Republican tax proposals on the table might increase income inequality, at least in the short term, according to William G. Gale of the Tax Policy Center and many other left-leaning and centrist economists.

Conservatives respond that high tax rates would stifle economic growth, at a minimum, and cause some businesses and high-income workers to flee to other countries. When top American tax rates were much higher, from the 1940s through the 1970s, businesses could not relocate as easily as they can now, say critics of Mr. Piketty and Mr. Saez.