Lagardere SCA, the French publisher of Dan Brown’s “The Da Vinci Code” and Elle magazine, agreed to buy Time Warner’s book unit for $537.5 million to become the world’s third-largest publisher.

The Time Warner Book Group is the fifth-largest American book publisher, with authors including James Patterson and Malcolm Gladwell, Paris-based Lagardere and Time Warner said in emailed statements yesterday.

Lagardere has been seeking takeovers to lower the company’s dependence on its stake in the maker of Airbus aircraft, and it acquired W.H. Smith Plc’s Hodder Headline unit for $389 million in September 2004. Time Warner has been selling divisions including its music unit to reduce debt, and said its book business needed the global “scale” of being part of a larger book publisher.

“This is a major step in fulfilling a Lagardere objective to create a balanced portfolio in three main languages, French, English, and Spanish,” said the statement from Lagardere, whose chief executive is Arnaud Lagardere.

Besides publishing its own titles, Time Warner Books acts as a distributor for third parties such as Walt Disney Company and Microsoft, the Time Warner statement said. The company operates in America, Britain, Australia, and New Zealand, it said.

“Lagardere are very, very aggressive,” said media analyst Theresa Wise of Accenture, citing such moves as the Hodder deal and the acquisition three years ago of part of publisher Larousse in France. The deal is also “geographically important” by making Lagardere a bigger player in American publishing, she said.

“Publishing is consolidating incredibly fast because it’s been a slow-growth industry for quite a while,” Ms. Wise said, citing the bid last year by British book retailer HMV Group Plc for smaller rival Ottakar’s Plc. The deal is awaiting regulatory approval.

Lagardere, France’s largest publisher, owns 15% of European Aeronautic Defense and Space Company, or EADS, which makes Airbus airplanes.

Shares of Time Warner rose 17 cents to $18.57 at 4:01 p.m. in New York Stock Exchange composite trading. The shares have gained 6.5% this year. Lagardere shares rose 20 cents to close at $80.46 in Paris.

“This is a terrific transaction that is the right thing to do for both the Time Warner Book Group and our shareholders,” the chairman and chief executive of Time Warner, Richard Parsons said in the statement.

The division performed well in 2005 and “is at the top of its game,” he said. “To build on this success, however, it needs the scale and other advantages that come from being part of a larger, more global book publisher.”

Time Warner Book Group added 16 titles to the New York Times bestseller list in the fourth quarter of 2005, the company said last week. Seven were at the no. 1 position, including James Patterson’s “Mary, Mary,” Nicholas Sparks’s “At First Sight,” and Michael Connelly’s “The Lincoln Lawyer.”