NEW YORK — US Secretary of State Hillary Clinton entered the 2012 US presidential campaign fray for the first time Monday, highlighting a burning issue at the center of debate -- taxing the wealthy.

"One of the issues that I have been preaching about around the world is collecting taxes in an equitable manner, especially from the elites in every country," Clinton told a glittering New York conference.

Winning some laughter at the forum on the sidelines of the UN General Assembly, she insisted: "You know I'm out of American politics, but it is a fact that around the world the elites of every country are making money."

Democratic US President Barack Obama, fighting for re-election in November, and his bitter rival, Republican Mitt Romney, have laid out starkly different visions for how to boost the struggling US economy.

Multi-millionaire former businessman Romney has proposed cutting income tax rates by 20 percent across the board, eliminating tax on investment income, and slashing the corporate tax rate.

Obama has said Romney's $5 trillion tax plan would mostly benefit the wealthy and force the US government to boost taxes on families with children by $2,000 (1,550 euros) per year.

Instead, Obama favors higher taxes for the nation's wealthiest.

Talking in general terms at the Clinton Global Initiative, Clinton insisted: "There are rich people everywhere and yet they do not contribute to the growth of their own countries.

"They don't invest in public schools, in public hospitals, in other kinds of development internally," she told the aid foundation set up by her husband, former Democratic president Bill Clinton.

But as countries seek to stop being aid recipients, Clinton said taxes were vital to "mobilize their own domestic resources for long-term development."

"And so it means for leaders telling powerful people things they don't want to hear," said Clinton.

"It means being transparent about budgets and revenues, and bringing corruption to light and when that happens, we shouldn't punish countries for uncovering corruption; we should reward them for doing so.

"And it means putting into place regulations designed to attract and protect investment."

Clinton, who was defeated by Obama in 2008 to be the Democratic presidential candidate, has so far ruled out a run in 2016.

On Sunday, Bill Clinton left the matter open, saying: "I have no earthly idea what she will decide to do."

"I think we ought to give her a chance to organize her life and decide what she wants to do," he added.