“Harry Potter” author J.K. Rowling succeeded in blocking publication of a Potter encyclopedia when a judge agreed yesterday that a fan and Web site operator who was ready to sell the guide had violated her copyrights.

A U.S. District justice, Robert Patterson, said Ms. Rowling had proven that Steven Vander Ark’s “Harry Potter Lexicon” would cause her irreparable harm as a writer. He permanently blocked publication of the reference guide and awarded plaintiffs Ms. Rowling and Warner Bros. Entertainment Inc. $6,750 in statutory damages.

Ms. Rowling said she was “delighted” with the ruling, adding, “I went to court to uphold the right of authors everywhere to protect their own original work. The court has upheld that right.” Warner Bros. also said it was pleased with the ruling.

Ms. Rowling and Warner Bros., maker of the Harry Potter films and owner of intellectual property rights to the Potter books and movies, sued Michigan-based RDR Books last year to stop publication of material from the Harry Potter Lexicon Web site. Mr. Vander Ark, a former school librarian, runs the site, which is a guide to the Potter books and includes detailed descriptions of characters, creatures, spells, and potions.

The small publisher was not contesting that the lexicon infringes upon Ms. Rowling’s copyright but argued that it was a fair use allowable by law for reference books. In his ruling, Mr. Patterson noted that reference materials are generally useful to the public but that in this case, Mr. Vander Ark went too far.

“While the Lexicon, in its current state, is not a fair use of the Harry Potter works, reference works that share the Lexicon’s purpose of aiding readers of literature generally should be encouraged rather than stifled,” he said.

He said he ruled in Rowling’s favor because the “Lexicon appropriates too much of Rowling’s creative work for its purposes as a reference guide.”