The New York Public Library’s largest new construction in recent memory, the Bronx Library Center, opened its doors to the public for the first time yesterday after a ribbon-cutting ceremony attended by Mayor Bloomberg, top library officials, local politicians, and the philanthropists Susan and Roger Hertog, whose donation helped make the library possible.

“Public libraries are everybody’s portal to growth and fulfillment in a democratic society,” the president of the New York Public Library, Paul LeClerc, said. Today “we inaugurate one of the single most important and most beautiful libraries in all of urban America.”

The $50 million Bronx Library Center is the flagship library in the borough for the New York Public Library, which oversees branches in Manhattan, the Bronx, and Staten Island. At 78,000 square feet, it triples the capacity of the Fordham Library Center, which has served as the Bronx’s main branch since it was built in 1923. A spokeswoman for the NYPL, Gayle Snible, said the old library might be converted into a specialty public high school.

“A library is a symbol of the principles of equality and freedom on which this great nation is based,” Ms. Hertog, who along with her husband contributed $5 million toward the branch’s construction, said at the ceremony. “A library is not an exclusive club. The librarians don’t ask you if you are rich or poor, or if your parents are American or not. They help you find what we want and need as if it were your birthright.”

Mr. Hertog is chairman of The New York Sun.

The new branch houses 200,000 books, periodicals, and recordings in its collection, which includes a bilingual, 20,000-book Latino heritage section. It provides 127 computers for public use, 30 additional laptop computers that can be used throughout the building, free wireless Internet access, and computer classes geared to all ages.

“Public education and libraries are great investments. The more opportunities young people have, the more they will live fulfilling and productive lives,” Ms. Hertog said in a telephone interview. “Roger and I grew up in modest circumstances and it was really the public schools and the libraries that gave us a chance for self-realization that we would otherwise never have had. Our desire to help fund the Bronx Public Library is an expression of our deep commitment to offering young people the opportunity to learn and grow.”

Ms. Hertog added that one reason she and her husband, who grew up in the Bronx, allowed their donation to be made public was “the hope it might inspire those who have the resources to follow the same path.”

Richard Dattner & Partners Architects designed the library to fit its trapezoidal lot and height setback requirements while maximizing light and views. With its use of natural light, energy-efficient systems, and recycled or renewable materials, it is the New York Public Library’s first “green” facility.

“This is a very necessary investment,” a former congressman of the Bronx who was chairman of the board of City University of New York, Herman Badillo, said. “Libraries are key to stimulating kids to study and to stay in school,” which is especially important in the Bronx, he said, where many cannot afford computers or even books.

“The whole way to eliminate poverty is very simple,” he added. “It’s not government. The answer is, good government is never going to provide jobs for all, or housing for all, or health care for all. But if you get a good education, then that’s the answer, because with a good education you can get a job, get your own housing, and provide for your own health care.”

Mr. Badillo came to New York from Puerto Rico as an impecunious orphan and, a product of public schools and libraries, became the first Puerto Rican member of Congress and the first Latino to be elected president of the Bronx and to serve as a deputy mayor of New York.

A professor of the history of the book at Drew University, Jonathan Rose, who chronicled the self-education of poor Britons in the 19th and early 20th centuries in “The Intellectual Life of the British Working Classes” (2001), told the Sun that libraries were among the most important public social programs.

“Whereas almost all other social welfare programs have been seriously question, such as Aid to Families with Dependent Children and so on, the one program that’s never questioned … is of course public libraries. They’re very cheap, all things considered. The benefits are enormous.They are used by people of all social classes, and for that reason I think they are a very popular institution – and deservedly so,” he said.