(Adds union statement, reaction from Ex-Im opponents)

By Andrea Shalal

WASHINGTON, July 29 (Reuters) - Boeing Co Chairman Jim McNerney on Wednesday said the aircraft maker is actively looking at moving "key pieces" of its operations to other countries given uncertainty about the future of the Export-Import Bank, whose charter expired on June 30.

"We are now forced to think about this differently," McNerney told hundreds of executives and diplomats during an interview hosted by the Economic Club of Washington.

McNerney, who retired as the company's chief executive on July 1, said Boeing might consider sites in countries that offer export credits, but gave no details about which operations could be affected or when the company had launched its review.

The International Association of Machinists District 751, which represents more than 30,000 Boeing workers, blasted McNerney's threat to move jobs overseas. "The only Boeing job that should leave this country is his," said Jon Holden, who heads Boeing's largest union.

America's largest exporter, Boeing employs 165,000 people.

"Boeing's fear mongering undermines the company's remarkable products and it won't win converts in Congress," said Dan Holler, spokesman for Heritage Action for America, a sister organization of the Heritage Foundation that promotes conservative policy and is one of the most vocal critics of the bank.

The Ex-Im Bank was created during the Great Depression to lend money to U.S. exporters and their foreign customers. Its charter lapsed after conservatives in the U.S. Congress cast it as a promoter of "crony capitalism" for multinationals such as Boeing and General Electric Co.

Hopes of reviving the trade bank were dashed on Tuesday as Congress moved toward a short-term extension of highway funding without a provision to renew the bank's charter. That means the bank's fate hangs in the balance through September or October, McNerney said.

Uncertainty about the availability of export credits is already weighing on sales of a range of Boeing products, including commercial satellites, according to sources familiar with the situation who requested anonymity because of the sensitivity of the business negotiations.

McNerney's comments reflect U.S. industry's growing frustration about deep partisan divides that have paralyzed Congress since the rise of the right-wing Tea Party in 2010 and the imposition of mandatory spending cuts that have hit revenues at the defense division of Boeing and other arms makers.

GE's chief executive, Jeff Immelt, last month told the Economic Club his company would move manufacturing jobs to Canada and Europe if the Ex-Im bank closed.