BANK RIVALS GLOBAL-IZING

Wall Street chief Jamie Dimon is getting a great 51st birthday gift – a $1 billion expansion and a sweet get-even moment with his former shop, Citigroup.

As Dimon yesterday unveiled J.P. Morgan Chase’s bold invasion into Europe and Asia, his ex-colleagues across town quietly disclosed a face-saving re-entry in Japan after its humiliating expulsion two years ago following a money-laundering scandal.

Citigroup said in filings yesterday it bid $10.8 billion to gain a bigger foothold in the world’s second-largest financial market by acquiring investment banking group Nikko Cordial, in which it already owns 4.9 percent. They are paying a heavy price to get back on track – a bid that’s 35 percent higher than Nikko’s market value just a week ago.

At least three top Citi executives walked the plank over the global black eye, but one ousted boss didn’t suffer that badly.

Thomas W. Jones, who headed money-management operations and was responsible for the Japanese offices at the time, got a $50 million private investment from Citigroup to start a new hedge fund after his ouster.

As for the Nikko deal – if Japan approves it – Citi will get 109 banking branches and 12,000 employees, plus $257 billion in client assets.

Dimon was openly pleased in talking about his ambitious expansion into Asia and other world capitals, but made no public mention of Citigroup’s woes. Insiders contend Dimon still harbors a few ill feelings about his betrayal at Citigroup, where he worked for 15 years before leaving in the wake of a string of conflicts with former chief Sandy Weill.

Dimon, who celebrates his birthday next Tuesday, said he’ll back up his global growth with a hiring spree in Asia and Europe.