Barack Obama answers questions from Twitter users on Wednesday but the US president is not confining his answers to 140 characters.

Obama will verbally answer questions posed on the short-messaging service during a "Twitter Town Hall" being streamed live from the White House at askobama.twitter.com.

The president's answers will also be condensed to fit Twitter's 140-character format and put out on the Twitter feeds @townhall and @whitehouse, which has more than 2.24 million followers.

Twitter co-founder Jack Dorsey will moderate the event, which begins at 2:00 pm (1800 GMT), choosing from the thousands of questions submitted on Twitter over the past week using the hashtag #AskObama.

The Twitter town hall was billed an opportunity to ask the president questions about jobs and the economy but queries have been pouring in on a variety of subjects both serious and flippant.

Users have asked when Obama would support gay marriage, a subject on which the president has said his position is still evolving, while others have asked about legalization of marijuana.

One user asked why he had not yet closed the Guantanamo Bay war-on-terror camp, and there were also questions centering on why America offered billions of dollars in aid to other countries while it had problems at home.

Obama's Republican foes swarmed Twitter hours before the event to blast his handling of the economy using the #AskObama hashtag, making their criticisms visible to participants in the discussion.

"#AskObama: if more gov't is good #4jobs, why are so many Americans still unemployed?" challenged Republican Darrell Issa, chairman of the House Government Reform and Oversight Committee.

"Will you take tax hikes off the table, or tell the American people how raising taxes will create jobs?" Republican House Speaker John Boehner said on his official @SpeakerBoehner Twitter feed.

Republicans, who control the House of Representatives, aimed to use Twitter feeds for key committees, leadership, and member offices in their social media counterassault, a Boehner aide said.

Obama pioneered the use of social media in his 2008 election campaign and is developing new techniques to reach voters without a media filter as he gears up his 2012 reelection drive.

He has previously answered questions submitted via YouTube and in April held a town hall-style event at the California headquarters of social networking giant Facebook.

"The purpose of doing this event is to try to find new opportunities to connect with Americans around the country," White House Director of Digital Strategy Macon Phillips said.

"We've entered a different information age, where people get news and information in a different way than they did in the past," added White House Communications Director Dan Pfeiffer.

"If you're going to communicate with the broad public, it is no longer sufficient to simply do it through traditional mainstream media," he said.

"You have to go beyond that because people are getting their information in different ways and from different sources," Pfeiffer said. "We're always on the lookout for ways to have a productive interaction with the public in new and exciting ways."