SANTA MONICA, Calif. &#8212 Vivendi SA said Sunday that it plans to acquire a controlling stake in Activision Inc. and combine the video game publisher with Vivendi Games in a deal the companies valued at $18.9 billion.

The combination of Santa Monica-based Activision, whose titles include “Guitar Hero,” “Call of Duty” and the “Tony Hawk” series, and Vivendi Games, which publishes “Crash Bandicoot” and owns the online role-playing franchise “World of Warcraft,” would create the world’s largest pure-play online and console game publisher, the companies said.

Under the agreement, shares of Vivendi Games will be converted into 295.3 million new shares of Activision common stock at a price of $27.50 per share, the companies said in a statement.

Vivendi, based in Paris, France, will purchase 62.9 million newly issued shares of Activision common stock at a price of $27.50 per share, giving Vivendi a 52 percent stake in the new company to be called Activision Blizzard.

After the transaction closes, expected in the first half of 2008, Activision Blizzard will launch a $4 billion all-cash tender offer to purchase up to 146.5 million Activision Blizzard common shares at $27.50 each.

Vivendi also has agreed to acquire an additional $700 million of newly issued Activision shares, giving Vivendi about a 68 percent stake in Activision Blizzard if the offer is tender offer is fully subscribed.

The offer price is a 24 percent premium over Activision’s closing price Friday of $22.15 per share.

Activision Blizzard will continue to operate as a public company and be traded on the Nasdaq Stock Market under the ticker ATVI.

The merger will provide Activision Blizzard with the most diversified and broadest portfolio of interactive entertainment assets in the industry, according to the statement.