WASHINGTON (AFP) - US Democratic presidential candidate Joe Biden said on Saturday (Sept 26) he expects "personal attacks and lies" from Donald Trump in their first televised debate on Tuesday, but showed confidence in his ability to stand up to him.

"It is going to be difficult," the former vice-president acknowledged in an interview broadcast on MSNBC.

"My guess is, it's going to be just straight attack. They're going to be mostly personal. That's the only thing he knows how to do," he said of the Republican president.

"He doesn't know how to debate the facts. He's not that smart," Biden continued.

"He doesn't know much about foreign policy, he doesn't know much about domestic policy. He doesn't know much about the detail."

As a result, Biden predicted, "it'll be mostly personal attacks and lies; but I think the American people are on to him."

The debate on Tuesday in Cleveland, Ohio will be the first time the 77-year-old veteran politician has faced the president he has promised to dethrone.

The men will meet again for two more debates before the Nov 3 election.

But some of his supporters fear that Biden, who is prone to blunders and slip-ups, may waver in these televised duels under the rhetorical blows of the Republican billionaire - who is also prone to blunders and slip-ups, but who is far more aggressive.

Trump himself never ceases to mock what he says is his rival's lack of dynamism, nicknaming him "Sleepy Joe" and attacking his mental acuity.

The Democrat, however, said he was prepared.

"People know the president's a liar," Biden said.

"It's not like it's going to come as a surprise. And so I'm prepared to go out and make my case as to why I think he's failed and why I think the answers I have to proceed will help the American people and the American economy, and make us safer internationally."