NEW ORLEANS (Reuters) - Singer Beyonce said she sang along to a pre-recorded track at the inauguration of President Barack Obama, but delivered a stirring a cappella version of the U.S. national anthem at a Super Bowl news conference on Thursday.

She also said would be singing live at the half-time show of the National Football League championship game between the San Francisco 49ers and Baltimore Ravens at the Superdome on Sunday.

Beyonce's performance of the "Star-Spangled Banner" at the January 21 inauguration ceremony sparked a debate over whether she had lip-synched her performance in Washington.

"I am a perfectionist and one thing about me is that I practice until my feet bleed and I did not have time to rehearse with orchestra," the Grammy-winning artist said on Thursday.

"It was a live television show and a very, very important emotional show for me and one of my proudest moments, and due to the weather, to the delay, due to no proper sound check, I did not feel comfortable taking the risk.

"It was about the president and the inauguration and I wanted to make him and my country proud, so I decided to sing along with my pre-recorded track, which is very common in the music industry, and I am very proud of my performance," she said.

Beyonce, 31, one of pop music's biggest celebrities, surprised the media on Thursday by asking them to rise at the start of her news conference and launching into a solo version of the U.S. national anthem.

After the applause in the room died down, she asked the hundreds of media representatives, "Any questions?"

Asked if she planned to sing live during the Super Bowl game, annually one of the most-watched TV events in the United States, the singer said: "I will absolutely be singing live. This is what I was born to do, it is what I was born for."

The NFL also said that Jennifer Hudson would perform "America the Beautiful" with the chorus from Sandy Hook Elementary School in Newtown, Connecticut, where 20 children and six adults were killed in a mass shooting in December.

Alicia Keys will sing the national anthem before the game's kickoff, while other artists, including OneRepublic and Matchbox Twenty, will be part of the televised pregame show.