WASHINGTON — Sandra Day O’Connor, the first woman on the Supreme Court, announced Tuesday that she has the beginning stages of dementia, “probably Alzheimer’s disease,” and will no longer be able to participate in public life.

And she is asking Americans to take up a cause near and dear to her -- civics education.

The 88-year-old said in a public letter that her diagnosis was made some time ago.

“While the final chapter of my life with dementia may be trying, nothing has diminished my gratitude and deep appreciation for the countless blessings in my life,” she wrote. She added: “As a young cowgirl from the Arizona desert, I never could have imagined that one day I would become the first woman justice on the U.S. Supreme Court.”

O’Connor was a state court judge before being nominated to the Supreme Court in 1981 by President Ronald Reagan, who fulfilled a campaign promise by nominating a woman to the Supreme Court. O’Connor had graduated third in her class from Stanford Law School and was the first woman to lead the Arizona state senate. She was 51 when she was unanimously confirmed to the high court. On the Supreme Court, her votes were key in cases about abortion, affirmative action and campaign finance as well as the Bush v. Gore decision effectively settling the 2000 election in George W. Bush’s favor.

O’Connor was 75 when she announced her retirement from the court in 2005. It was a decision influenced by the decline in the health of her husband, John O’Connor III, who himself had been diagnosed with Alzheimer’s disease.

O'Connor also made civics education her cause celebre in the years after her retirement. She created a program called iCivics, which used free online interactive games and a curriculum to make civic learning more effective for middle and high school students. O'Connor said the program reaches half of the country's young people. Her hope is that this program continues.

"There is no more important work than deepening young people's engagement in our nation," O'Connor wrote.

"It is my great hope that our nation will commit to educating our youth about civics, and to helping young people understand their crucial role as informed, active citizens in our nation," she wrote. " To achieve this, I hope that private citizens, counties, states, and the federal government will work together to create and fund a nationwide civics education initiative. Many wonderful people already are working towards this goal, but they need real help and public commitment."

Chief Justice John Roberts said in a statement that he was “saddened to learn” that O’Connor “faces the challenge of dementia.”

“Although she has announced that she is withdrawing from public life, no illness or condition can take away the inspiration she provides for those who will follow the many paths she has blazed,” Roberts wrote.

The Associated Press contributed to this story.