The Utah lawmaker said he deleted the tweets and hopes they will not hurt anyone else's feelings.
On Tuesday, the Eagle Mountain Republican tweeted in reference to Sterling's ouster as owner of the Clippers after making racially intolerant comments that "we should have known Don Sterling was a racist when he gave money to the National Association for the Advancement of Colored People."
Lifferth followed that up, saying: "Yes, any group that tries to advance specific people based of their race is by definition racist."
Jeanetta Williams, president of the Salt Lake Chapter of the NAACP, had said Lifferth's comment "shows his ignorance of the history of the NAACP."
Williams said late Thursday that she was happy Lifferth had apologized.
"I'm sorry that it happened to begin with, but we will accept his apology," she said. "I think he learned how insensitive his statements were … and I think he also found out that there was a lot of support for the NAACP, people he probably didn't even think were supporters of the NAACP or knew of our work."
Lifferth did not return a phone message Thursday night seeking comment.
Earlier Thursday, Lifferth had posted selected emails supporting and condemning his comments, including one from a state legislator whose name he withheld. He since deleted those messages.
Last year, Lifferth posted an email exchange with Williams in which he called himself "a hero of the civil rights era," explaining that his first-grade class in Nashville, Tenn., was the first integrated class in the county in 1971 and he was one of the few white students who attended classes on that first day.
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