A 78-year-old retired Los Angeles schoolteacher said she was breaking a lifetime of silence to announce that she is the illegitimate mixed-race daughter of former U.S. Sen. Strom Thurmond, R-S.C., once the nation’s leading segregationist.

In an interview, the woman said that Thurmond privately acknowledged her as his daughter and provided financial support since 1941.

Essie Mae Washington-Williams described her claims in a lengthy telephone interview last week, saying she protected Thurmond because of their mutual “deep respect” and her fears that disclosure would embarrass her and harm his political career. Thurmond, who died in June at age 100, said late in life through his office that Williams was a friend.

Williams, whose mother worked as a maid in the Thurmond family home as a teenager, has long been the subject of widespread speculation and has been pursued by journalists seeking her story for two decades. She always denied that she was Thurmond’s daughter.

“I want to bring closure to this,” said Williams, who plans to have a news conference Wednesday in Columbia, S.C. “It is a part of history.”

Williams did not provide definitive proof that she was Thurmond’s daughter. Her attorney, Frank Wheaton of Los Angeles, said she was ready to submit to DNA tests if challenged by the Thurmond family. Williams said she had documents to validate her claim, including cashier’s check stubs, mementos from Thurmond and a letter from an intermediary who delivered money from the senator. Williams declined to name the intermediary, citing privacy concerns.

Wheaton said Williams would “go to whatever lengths we must” to prove her story. As a sample of her documents, she provided The Post with a copy of a 1998 Thurmond letter thanking her “for the nice Father’s Day note you sent me.” Williams said she did not want to release additional documents at this time.

Williams’ claim comes as the attorney for the Thurmond estate, J. Mark Taylor, is overseeing settlement of the senator’s estate in Columbia, S.C. Thurmond bequeathed cash and other items, including clothing and real estate holdings, to his three surviving children with estranged wife Nancy Moore Thurmond.

“We are not seeking to challenge the wishes of the late senator with regard to his estate,” said Wheaton, who has been joined by Columbia attorney Glenn Walters in representing Williams. “Let’s be emphatically clear: We are not looking for money. We are merely seeking closure by way of the truth for Essie Mae Washington-Williams.”

Taylor said he has had no contact with Williams. Thurmond’s will did not acknowledge Williams or her heirs. Williams has struggled financially over the years, and in 2001, court records show, she declared personal bankruptcy.

Strom Thurmond Jr. did not return a phone call seeking comment. In interviews over the years, Thurmond’s sisters and staff have repeatedly said that Williams was only a family friend.

Williams said she met with Thurmond and received money at least once a year in sessions arranged by his Senate staff. In recent years, as the senator’s health declined, Williams said, financial assistance was passed through a prearranged conduit, a Thurmond relative in South Carolina. Williams’ attorney declined to specify the amounts of money she received, saying that information would be provided later.

Williams’ account resurrects one of the oldest stories in 20th-century southern political folklore. Over the years, Thurmond had called the allegation that he fathered a mixed-race child too unseemly to warrant comment. Noted political writer Robert Sherrill described an alleged daughter without providing a name in a 1968 book. The Post identified Williams by her maiden name in 1992, in a lengthy account of Williams’ relationship with Thurmond. The article reported that “both Thurmond and the supposed daughter have denied that he is her father, and no one has provided evidence that he is.”

Recently, Williams said media pressure has intensified, with interview requests from every major television network. She declined, consistently calling Thurmond a “family friend” who had merely provided her with financial assistance.

“I did not want anybody to know I had an illegitimate father,” said Williams, who has four grown children. “My children convinced me to tell the truth. I want to finally answer all of these questions … that have been following me for 50 or 60 years.”