NEW YORK - He's the leader of the free world, and he's won a Nobel Peace Prize. But only now, by one measure, is Barack Obama finally truly famous:

He's written a children's book.

With "Of Thee I Sing: A Letter to My Daughters," a picture book for readers three and up that hit bookstores Tuesday (it was announced in September), the president joins a long list of famous folk who've penned children's books: Madonna, John Travolta, Katie Couric, Will Smith, Paul McCartney, Whoopi Goldberg, Jamie Lee Curtis, Jay Leno, Jerry Seinfeld, Steve Martin, John Lithgow.

Even Obama's current secretary of state, Hillary Rodham Clinton, wrote one - when she was first lady, a book of children's letters to White House pets. The late Ted Kennedy wrote about Washington as viewed by his dog. On the other side of the political spectrum, conservative commentator Glenn Beck published a Christmas picture book last year, and Lynne Cheney has written several children's books.

Obama, who is donating his proceeds to a scholarship fund for children of disabled and fallen soldiers administered by the Fisher House Foundation, isn't even the only president to pen a children's book. Theodore Roosevelt and Jimmy Carter wrote books for young people, and John F. Kennedy had a young readers edition of his "Profiles in Courage."

Obama actually wrote "Of Thee I Sing" in 2008, after he was elected but before taking office, publishers said in September. It is illustrated by Loren Long, whose many credits include writing and illustrating the children's stories "Otis" and "Drummer Boy."

The book, published by Alfred A. Knopf Books for Young Readers, an imprint of Random House Children's Books, was already selling well Tuesday - it was No. 3 on Amazon.com's children's best-seller list, and No. 15 on the site's overall list.

But Obama, whose previous works are million sellers ("The Audacity of Hope" and the memoir "Dreams From My Father") wasn't the top-ranked presidential author on the overall list: George W. Bush's "Decision Points" was No. 1.

On the cover of "Of Thee I Sing" is a whimsical drawing of Malia and Sasha, skipping along with Bo, their beloved dog.

"Have I told you lately how wonderful you are?" the book begins. It proceeds to celebrate 13 American heroes and heroines.

"Have I told you that you are creative?" Obama asks, before describing painter Georgia O'Keeffe, who "helped us see big beauty in what was small."

Albert Einstein, Obama writes, "turned pictures in his mind into great advances in science." Jackie Robinson, the pioneering black major league baseball player, "showed us all how to turn fear to respect and respect to love."

Sioux leader Sitting Bull, he writes, "healed broken hearts and broken promises." Singer Billie Holiday "sang beautiful blues to the world."

Hellen Keller "taught us to look at and listen to each other." Maya Lin designed the Vietnam Veterans Memorial "to thank the many who fought for equality." Jane Addams, the social reformer and philanthropist, "opened doors and gave people hope."

Also honored is Martin Luther King Jr., who "gave us a dream that all races and creeds would walk hand in hand," and astronaut Neil Armstrong, whose lunar leaps "made us brave enough to take our own big, bold strides." Cesar Chavez "showed farmworkers their own power when they felt they had none."

Finally there are two former presidents: Abraham Lincoln, who "promised freedom to enslaved sisters and brothers," and George Washington, who "helped make an idea into a new country."

"Have I told you that they are all a part of you?" Obama asks at the end, as he walks off into the distance with his daughters.

It's not unusual that Obama, a successful author already, would want to write a children's book - presidents often like being associated with the cause of literacy, says Leonard S. Marcus, a historian of children's books. Obama, he says, is effectively using the device of writing to his own daughters as a way of speaking to all children. "He has something to say," Marcus says. "He has a sense of history, and of the hunger for role models."

Marcus likens Obama's book to a cross between Roosevelt's book of letters to his children and Kennedy's book, which emphasized heroes. The president's goals in writing it clearly differ, he says, from that of some celebrities, who write children's books as sort of a publicity stunt.

"It helps get the authors on TV," says Marcus, author of "Minders of Make Believe." ''And publishers use these books as a way to lure customers into the bookstores, hopefully to buy something else." Among the more respected celebrity children's authors, he says: Jamie Lee Curtis and John Lithgow.

The 40-page "Of Thee I Sing," with a list price of $17.99, is part of a $1.9 million, three-book deal with Random House reached in 2004, according to a disclosure report filed in 2005, when Obama was a U.S. senator from Illinois. The other two books were nonfiction.