United States President Barack Obama [Images] tried to play down the blooper made by Chief Justice John Roberts during the swearing-in ceremony, saying the top judge helped him on a few stanzas of the oath and the entire ritual went off 'relatively smoothly'.

"We were up there... we have got a lot of stuff on our minds and he, actually, I think helped me out on a couple (of) stanzas there. So overall I think it went relatively smoothly and I am very grateful to him," Obama told the ABC News after attending the Neighbourhood Ball in Washington.

It was the first of the 10 inaugural balls that he and his wife Michelle attended after he was sworn in as the nation's 44th President.

In a goof up that was watched by over two million people at the National Mall and by millions others watching the inauguration on television, Roberts fumbled as he switched a few words in the 35-word oath.

As Roberts began to administer the oath, Obama responded before the Chief Justice had completed the first phrase.

Obama ended up saying the first four words -- 'I, Barack Hussein Obama' -- twice. Then Obama paused abruptly after Roberts reversed a few words in the sentence 'That I will faithfully execute the office of the president of the United States', putting 'faithfully' at the end of the sentence.

Obama waited for Roberts to correct the words, realising that something was out of order. The top judge gave it another try, but this time, omitted the word 'execute'.

The goof up has become a hot topic of discussion and scrutiny, with TV channels and websites here galore with stories on how the Chief Justice could forget 35 words written in the country's constitution.

Obama also did not encourage the joke Vice President Joe Biden made earlier about Roberts' 'memory'.

Biden, who had to administer the oath of office to the senior executive staff at a White House ceremony, joked that he did not have a good memory as Roberts.

"My memory is not as good as Chief Justice Roberts," he quipped. Obama kept a straight face and was clearly not amused by Biden's words.