UPDATE 2-Bain says aims to buy Japan ad agency Asatsu-DK for $1.4 bln

* Bain plans to buy all the shares in Asatsu-DK

* Asatsu-DK's current top shareholder is WPP

* Asatsu-DK has asked WPP to cancel alliance (Recasts to attribute to Bain announcement, add details of transaction)

TOKYO, Oct 2 (Reuters) - U.S. private equity firm Bain Capital said it aims to buy 100 percent of Japan's third-largest advertising agency, Asatsu-DK Inc, for 152 billion yen ($1.35 billion), in one of the largest buyouts in Japan this year.

Bain said in a statement on Monday it plans to buy all of Asatsu-DK's shares from existing shareholders, including top shareholder WPP, for 3,660 yen a share, a 15.4 percent premium over Monday's close.

The private equity firm said it will launch a tender offer on Tuesday, and plans to delist the company. It said the buyout will be canceled if it fails to buy a stake larger than 50.1 percent.

Bain Capital's bid for Asatsu-DK comes just days after a consortium led by Bain signed an $18 billion deal to buy Toshiba Corp's chip unit.

WPP, the world's largest advertising group, owns 24.96 percent in Asatsu-DK. Asatsu-DK said in a statement it has requested WPP to terminate the capital alliance it made with WPP in 1998, under which Asatsu-DK and WPP set up joint ventures and cultivate clients together.

Whether WPP will sell its Asatsu-DK stake upon its request is not certain yet, said Shinpei Ishida, department director of the president's office for Asatsu-DK.

Asatsu-DK said it will sell its WPP stake worth 65.4 billion yen as of Friday and expects to post a special gain from the sale.

"Looking back over the past two decades, we made a certain achievement at the initial stage...," Asatsu-DK said about the alliance with WPP. "Since then we failed to find concrete measures that could be beneficial for both of us. We also failed to create synergies through our collaboration." ($1 = 112.7900 yen) (Reporting by Junko Fijita; Additional reporting by Chris Gallagher and Chang-Ran Kim; Editing by William Mallard and Muralikumar Anantharaman)