Sonia Sotomayor, Joe Biden Oath Of Office Administrator, Had Train To Catch

(Adds Supreme Court comment)

WASHINGTON, Jan 20 (Reuters) - Sonia Sotomayor had one eye on the door when she administered the oath of office to Vice President Joe Biden on Sunday.

Apart from officially swearing in Biden for his second term in office, the Supreme Court justice had other business to attend to: signing copies of her new autobiography at a New York City bookstore a few hours later.

Biden's office scheduled the swearing-in for 8 a.m. EST/1300 GMT to allow Sotomayor, the first Hispanic on the nation's highest court, enough time to catch a train for a three-hour ride to New York.

On Sunday at 2:30 p.m./1730 GMT, Sotomayor had been due to speak at a Barnes & Noble bookstore in Manhattan and sign copies of her memoir, "My Beloved World."

Her schedule was squeezed, however, when the private ceremony at the vice president's Naval Observatory residence began more than 20 minutes late after a Mass for Biden's friends and family.

Before Sotomayor departed, Biden made clear he appreciated her sticking around to give him the oath of office.

"I wanted to explain to you what a wonderful honor it was and how much out of her way the justice had to go," Biden said after the short event, attended by family and about 120 guests.

"She is due in New York. She has to leave right now, so I apologize," Biden said. "We are going to walk out, you see her car's waiting so she can catch a train I hope I haven't caused her to miss."

Despite the time pressure, Sotomayor delivered the vice presidential oath impeccably - unlike Chief Justice John Roberts, who mixed up the words to the shorter presidential oath when he swore in Barack Obama as president in 2009.

Sotomayor made the book signing in New York and read out a chapter to some 200 people about her parents and childhood in the Bronx.

She said she was "deeply touched" by the people who had waited at the bookstore for hours to see her. "That's an awesome amount of love to feel."

Supreme Court spokeswoman Kathy Arberg said the book event was a longstanding commitment that Sotomayor could not break.

Roberts swore in Obama for the president's second term just before noon on Sunday, the day mandated by the Constitution for the president's official term to begin.

The two men, plus Biden and Sotomayor, will do it all one more time on Monday, at a public inauguration ceremony on Capitol Hill in front of a crowd that Washington officials say could reach 800,000 people. (Reporting by Alistair Bell, Roberta Rampton and Joan Biskupic in Washington and Terry Baynes in New York. Editing by Christopher Wilson)