Big Bird, Donald Trump feature in debate

(AAP)

(AAP)

Big Bird would go, but Donald Trump might get a tax break under a plan to cut the ballooning US deficit outlined by Republican Mitt Romney.

Big Bird would go, but Donald Trump might get a tax break under a plan to cut the ballooning US deficit outlined by White House hopeful Republican Mitt Romney.

Former Massachusetts governor Romney duelled with incumbent President Barack Obama in the campaign's first face-to-face debate in Denver, Colorado on Wednesday.

Obama, a centre-left Democrat, charged that Romney's plan to enact a $US5 trillion ($A4.92 trillion) across-the-board tax cut for everyone, including the very wealthy, would not reduce the nation's debt but add to it.

"Governor ... it is not possible to come up with enough deductions and loopholes that only affect high income individuals to avoid either raising the deficit or burdening the middle class. It's - it's math. It's arithmetic," Obama said.

Romney denied he wanted to cut $US5 trillion in taxes, speaking instead of a 20 per cent across the board cut.

He said he would make up the difference by closing tax loopholes and reducing government programs, while boosting revenues by creating more jobs.

One program he would cut would be subsidies to the Public Broadcasting Sytem (PBS), which broadcasts popular children's program Sesame Street.

"I love Big Bird ... But I"m not going to keep on spending money on things to borrow money from China to pay for it," Romney declared.

The handle FiredBigBird was quickly created on Twitter and amassed some 13,000 followers before the end of the debate.

On Donald Trump, Obama argued that Romney's tax cut program would not only benefit small businesses but also real estate magnate Donald Trump, who is also considered a small business.

Romney retorted: "It's not just ... Donald Trump you're taxing; it's all those businesses that employ one quarter of the workers in America."