WASHINGTON — The Supreme Court on Monday refused to revive a challenge to Google’s digital library of millions of books, turning down an appeal from authors who said the project amounted to copyright infringement on a mass scale.

The Supreme Court’s brief order left in place an appeals court decision that the project was a “fair use” of the authors’ work, ending a legal saga that had lasted more than a decade.

In 2004, Google started building a vast digital library, scanning and digitizing more than 20 million books from the collections of major research libraries. Readers can search the resulting database, Google Books, for keywords or phrases and read some snippets of text.

The Authors Guild and several writers sued Google in 2005, saying the digital library was a commercial venture that drove down sales of their work. In their petition seeking Supreme Court review, they said “this case represents an unprecedented judicial expansion of the fair-use doctrine that threatens copyright protection in the digital age.”