Hundreds lined up outside the Union Square Barnes & Noble this morning for Hillary Rodham Clinton to sign their copies of her book, "Hard Choices," which went on sale Tuesday.. Clinton's highly orchestrated appearance in the liberal stronghold was thought by many to be a toe-dipping into the waters of a 2016 presidential campaign.

"I want her to run for president," said Marilyn Moorcroft, 71, of the West Village. "She will be a terrific president."

The book offers a glimpse into her four years as head of the Department of State in the Barack Obama administration, Clinton told admirers - some of whom had camped out overnight for a chance to see her - at her 11 a.m. book signing.

"It's written for anybody who wants to think about and learn about what is happening in the world today, why America matters and why the world matters to America," Clinton before her book signing. "And we have a lot of hard choices ahead of us that continue to make it as great and strong as it should be."

The wait to see the former first lady was more than five hours for many, who were subjected to seemingly endless security precautions. After waiting in line outside, they were allowed in small groups into the first floor, where each customer had to buy a book and received a wrist band. The crowd then baby-stepped in formation to the second floor on escalators that had been turned off, where they surrendered all their purses,bags and other personal items,and waited another hour. Ushered to the third floor, they waited again to be wanded by security personnel. Finally, they progressed up the still escalators to the fourth floor. There, Clinton sat on a stage wearing a fuchsia skirt suit and chunky necklace. She signed "Hillary" on the fly leaf of copies of "Hard Choices," which were towered in stacks beside her, shaking hands with well wishers. An assistant nearby then handed the customer a signed copy as they were coaxed to move along.

Outside, an orderly line stretched along East 17th St. and around the corner to Park Avenue South.

While Clinton has yet to declare whether she's running for president in 2016, most in line - some wearing buttons saying "I'm ready for Hillary" - were clearly hoping she'd throw her hat in what will likely be a very crowded ring.

Joe Cassar, 62, a retired insurance executive of Murray Hill, sees Clinton's book tour as a start to her presidential rum.

"Of course this is a campaign," he said. "I'm a Democrat. I want to see what her positions are and where she stands."

And if given the opportunity to pose a question to Clinton at the book signing, Cassar said he'd ask if she'd continue Obamacare and whom she'd pick for her cabinet.

Many hoped for the chance to make a memory to cherish and share by shaking the hand of a woman who might become the country's first female president, but they acknowledged they would probably have little chance of a meaningful interaction with one of the most famous women in the world.

Maria Karidis, 37, of Astoria wanted to ask the former secretary of state, "what can you do to help the Greece economy?"

Not the U.S. economy?

"Corporations already own the United States," Karidis responded.

Workers for readyforhillary.com were soliciting admirers to sign up as volunteers for a Hillary Clinton presidential campaign. "So far, I've got four pages of names," said intern Nico Bonder.

Her candidacy "is a fait accompli at this point," observed Marc Fenton, 49, a freelance life coach who lives in Union Square. Fenton, who uses a motorized scooter, was a bit miffed by the exacting security protocols to see the former first lady. "Eight years ago, to see (Barack) Obama, it was very straight forward," and he was allowed to go to the front of the line, he noted. "Obama walked into the room, noticed me on my scooter and shook my hand before he greeted anyone else," recalled Fenton, who wondered if he would be accorded the same courtesy by this potential presidential candidate.

The crowd was full of Democrats, but not everyone in line was a die-hard Hillary fan.

M. Saidia McLaughlin, 63, a retired educator from "the proud Republic of Brooklyn" popped by after not being able to find "Hard Choices," at The Strand bookstore nearby. While she would support Clinton should she become the Democratic nominee, McLaughlin said Elizabeth Warren and Maria Shriver topped her list of preferred candidates.

The Clintons, she said, "threw a lot of women under the bus," such as legal professor Lani Guinier, whose nomination for a federal civil rights post was withdrawn by then-President Bill Clinton, and ex-surgeon general Dr. Joycelyn Elders, who Bill Clinton fired after speaking frankly about contraception, masturbation and legalizing drugs. "Even the women in the welfare program! I'd ask her how did she let her husband marginalize women?" McLaughlin said.

Zarine Ali, 32, a geology graduate student at Brooklyn College, said she was hoping to get a signed copy of Clinton's book to give to her 5-year-old niece. "She'll take New York for sure," Ali said of the primaries. Clinton "has really proven herself," as a politician and deserves a crack at being president, said Ali. Coming to the book signing was a way for Ali to show her support. Clinton, she postulated, "probably wants to see how many people show up," to gauge her likelihood of winning. -- with Lauren Holter and Emily Ngo