The library's main Manhattan building, a research facility at Fifth Avenue at 42nd Street known as the Humanities and Social Sciences Library and the site of the announcement, will be renamed the Stephen A. Schwarzman Building.
Schwarzman, the son of a linen and curtain store owner who attended Yale University and Harvard Business School, said the library, which was created in 1895, "is a passport to the American dream for lower- and middle-income Americans and immigrants from around the world."
"It's a free university for everyone, from children to scholars," said Schwarzman, a library trustee. "I've always loved this library, particularly for the way in which it serves all people and entirely without cost to them."
The plan will be financed by the library from sales of real estate, private donors and city, state and federal funds. More than $250 million, including Schwarzman's gift, has been raised, the library said.
The plan includes renovating the Fifth Avenue building, which opened in 1911, and adding a lending division there; creating state-of-the art hub libraries in Manhattan and Staten Island; refurbishing branches; and expanding the library's online services and upgrading technology, particularly computers.
Visits to the library's 89 locations increased in fiscal year 2007, when there were more than 16 million, or 2 million more than in 2006, the library said. The library's Web site received more than 25 million visits in fiscal year 2007, 5 million more than in 2006.
Mayor Michael Bloomberg, City Council Speaker Christine Quinn, Nobel laureate Toni Morrison and library chairman Catherine C. Marron and president Paul LeClerc also attended the announcement.
"In a world increasingly impacted by the Internet and globalization, it is essential to New York City's future that its library system be among the world's best," LeClerc said. "This plan will make that dream a reality."
