NEW YORK (Reuters) - American International Group Inc Chairman Robert Willumstad said one of the first things he did after being named chief executive was to reach out to former CEO Maurice (Hank) Greenberg, a large AIG shareholder who has had an acrimonious relationship with the insurer since leaving three years ago.

Willumstad, who was installed as chief executive late on Sunday, said he telephoned Greenberg and the two planned to meet this week, as long as schedules permitted.

A meeting could begin to mend a rift between AIG and its former leader. Greenberg has in recent months been scathing in his criticism of AIG's board and management, and there are numerous lawsuits outstanding between the two sides. Greenberg left AIG in 2005 under the cloud of an accounting scandal, and is still fighting civil charges stemming from those events.

Willumstad, who replaces Greenberg's successor, Martin Sullivan, in an investor call early on Monday, vowed to move swiftly to straighten things out at AIG, which has been badly hit by market losses from bad mortgage bets. He described himself as a "hands on" manager.

AIG's shares are trading below half the value they held a year ago, after larger-than-expected write-downs on assets linked to subprime mortgages.

Willumstad, a former Citigroup executive, said over the next three months he will put together a turnaround plan, and expects to present it to investors in early September. He did not rule out shedding businesses that no longer fit into the sprawling AIG group, but did not foresee breaking the company apart.

The company operates in more than 100 countries, and apart from insurance, its businesses include asset management, financial products and aircraft leasing.

"Nothing is off the table, and there will be no sacred cows," said Willumstad.

The company is also looking for a new chief financial officer, after Steven Bensinger last month said he would step aside. Willumstad on Sunday told Reuters the company's search is already well under way, and external candidates with financial services experience are being considered.

Willumstad said investors should not read the management change as a sign of what will be reported in second quarter, calling the change "entirely unrelated" to those results, with the quarter due to end in a few weeks.

AIG, over the past two quarters, has reported consecutively worse results, the poorest in the firm's 89-year history.

AIG is expected to release second-quarter results in early August, and Willumstad says he has no plans for a delay.

AIG shares were down 1 percent at $33.82 in early trading on the New York Stock Exchange.

(Reporting by Lilla Zuill; Editing by Steve Orlofsky)