James Hadley Billington, a leading Russia scholar in 1987 when President Reagan nominated him to be the 13th Librarian of Congress, will step down from his post on Jan. 1 after nearly three decades leading the world’s largest library, officials announced on Wednesday.

In a statement, Mr. Billington said he had informed President Obama and members of Congress of his intentions to leave an institution that is one of the central repositories of American cultural history.

“Over the years I have been asked if I have been thinking about retiring; and the answer has always been ‘not really,’ because this library has always been not just my job, but my life,” Mr. Billington said in the statement. “However, I have never had more faith in the leadership and staff of the Library of Congress.”

The move comes after Mr. Billington, who turned 86 on June 1, presided over a series of management and technology failures at the library that were documented in more than a dozen reports by government watchdog agencies.

In a 2013 audit, the library’s inspector general warned that millions of items, some from as far back as the 1980s, remained piled up in overflowing buildings and warehouses, virtually lost to the world. In addition, just a fraction of its 24 million books are available to read online, 200 years after Thomas Jefferson laid the foundation for a vast national library by selling Congress his personal collection of books after the War of 1812.

The latest government investigation, delivered in March, accused the library of “widespread weaknesses” in managing its technology resources and cited a “lack of strong, consistent leadership” in that area. That report, and other recent complaints about Mr. Billington’s leadership, had recently caught the attention of the library’s congressional patrons.

“I am aware of the concerns that have been raised,” Senator Roy Blunt, Republican of Missouri, said in a statement before Mr. Billington’s retirement was announced. “We will be looking into this and other aspects of the library operations in the coming months.”

In addition, there has been mounting criticism from former staff members and other libraries that the Library of Congress, which has long occupied a singular place as the premier institution responsible for collecting and cataloging the world’s intellectual and cultural knowledge, is becoming increasingly irrelevant in the digital age.

“All librarians sense is a vacuum, a lack of leadership that concerns the whole world of learning,” Robert Darnton, the director of the Harvard University Library and a former colleague of Mr. Billington’s when they taught at Princeton.

Before Wednesday’s announcement, Mr. Darnton said: “I think that James Billington should resign. We should have a new librarian of Congress.”

In interviews, current and former library employees and others who have worked with Mr. Billington over the decades say they no longer recognize the charismatic, energetic librarian they once knew. They say he has slowed down so much that he rarely comes in before noon or works a full week in his majestic, sixth-floor office overlooking Capitol Hill and the Supreme Court. Co-workers said that he does not use email and that they often communicate with him through a fax machine at his house.

But Mr. Billington’s supporters say he has continued to carry out the library’s missions with vigor. David McCullough, a Pulitzer Prize-winning historian and longtime friend, called Mr. Billington a “man of infinite interests and extraordinary ideas.”

In a telephone interview last week, Mr. Billington said that he had no intention of retiring, and that the criticism of him has come from rivals and disgruntled former employees.“Let me emphatically say that I am still involved in every major decision at the library,” Mr. Billington said. “I don’t know where you are getting this kind of gossip.”

In a statement announcing his departure, the library noted that Mr. Billington had created two online portals for the library, including the World Digital Library, with about 11,000 items. The statement noted that collections grew from 85.5 million items in 1987 to more than 160 million items today.

The statement said Mr. Billington is “recognized for having brought the world’s largest library into the digital age.”

But Mr. Darnton and other university librarians insist that Mr. Billington is stuck in a past era and has resisted their entreaties to cooperate on a large-scale digitization of the library’s 160-million item collection. They say the vast majority of the library’s archives remain largely closed off from digital information seekers, stored on physical shelves the way they have been for decades.