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Hillary Clinton on Wednesday picked up the endorsement of the billionaire investor Warren Buffett, who gave his backing to her while calling for increased taxes on the country’s highest wage earners.

Mr. Buffett began his remarks at an event in Omaha with some stark statistics. In 1992, the top 400 wage earners in the United States made an average of $48.6 million each, compared with $335.7 million in 2012, Mr. Buffett said, using the most recent statistics available based on income tax returns.

“This group,” which includes Mr. Buffett, who is worth an estimated $66.7 billion, “had their income increase sevenfold,” he said, adding, however, that “their tax rate has fallen to 16.3 percent, so they got a one-third tax cut as their income went up 7 to 1.”

Mr. Buffett did not support a candidate in the 2008 Democratic contest, despite being courted by Mrs. Clinton and Barack Obama, who were then senators. (“I told both of them that if they ran for president, I’d support them and here we are,” Mr. Buffett said during that heated battle.)

But on Wednesday, Mr. Buffett, the chief executive of Berkshire Hathaway, said he was endorsing Mrs. Clinton because she “will make sure that those people who are having to work two jobs to barely get by will not have that kind of world for themselves and their children moving forward.”

Mrs. Clinton nodded in agreement. “I want to be the president for the struggling, the striving and the successful,” she said.

To do that, she has proposed a wide and varied agenda of domestic policies including tax-credits for middle-class families that are caring for sick or elderly relatives or are sidled with steep healthcare costs; a $350 billion plan to make college more affordable; a $250 billion plan to improve the country’s infrastructure while creating jobs; and a plan for universal prekindergarten that could cost tens of billions of dollars, among other proposals.

Aides have said that those plans would be paid for by tax increases on the wealthy, the closing of corporate tax loopholes and other changes in the tax code. Last week, Mrs. Clinton released a plan to crack down on “inversions,” or the practice of United States corporations to merge with smaller foreign companies in order to pay a lower tax rate.

Mrs. Clinton’s campaign used the event Wednesday to signal to the national news media that she would eventually call for an additional tax increase on Americans who earn more than $250,000 a year. (“Clinton to propose further tax increases on wealthy Americans at Buffett event,” a headline on CNBC read.) But other than praising Mr. Buffett’s remarks and expressing support for the “Buffett rule,” which calls on the richest American to pay more taxes, Mrs. Clinton did not discuss taxes in any detail.

Aides have long signaled that she would not shy away from raising taxes on the wealthiest earners. “She will make sure the wealthiest Americans finally start paying their fair share, not force the middle class to pay even more than they already do,” Brian Fallon, a campaign spokesman, said last month.

But on Wednesday, Mrs. Clinton, with a major new supporter at her side, recited her recurrent theme of trying to connect financial turmoil to Republican policies. “Our economy does better when we have a Democrat in the White House,” she said. “That is just a fact.”

She was quick to add: “I am not running for my husband’s third term. I am not running for Barack Obama’s third term. I am running for my first term.

“But I am going to do what works for our economy.”

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