A bitter lobbying battle between corporate titans Boeing Co. and Delta Air Lines Inc. has ensnared a small agency playing a big role in the Obama administration's drive to boost exports.

The White House has tried unsuccessfully for months to get Congress to renew and expand the lending authority of the Export-Import Bank, which provides loan guarantees and other assistance to overseas customers of U.S. companies at below-market rates.

The bank -- overseen by a White House appointee and funded by customer fees and interest payments -- has doubled its financial support in the past four years to US$41 billion annually. But without congressional action, the bank may soon hit its limit.

That's sparked alarm at Chicago-based Boeing, the bank's top beneficiary, which is leading the corporate charge in support of the administration's efforts to renew and expand lending. The bank has helped finance billions of dollars in sales of Boeing aircraft to foreign customers.

One of those customers is Air India, which until 2008, competed directly with Delta on the New York to Mumbai route. But Delta stopped flying the route, which it had switched to Atlanta, saying it couldn't compete with Air India's fares.

Now, Atlanta-based Delta is pushing hard for a curb on the bank's activities.

Boeing's position is shared by the U.S. Chamber of Commerce, the National Association of Manufacturers and the Business Roundtable, an association of chief executive officers, as well as numerous lawmakers whose districts include Boeing plants. They argue the bank enables deals to go through that otherwise wouldn't, boosting business and U.S. jobs.

The bank is "critical to continuing on the path of growing exports," said Francisco Sanchez, the Commerce Department's undersecretary of international trade. "I've heard of one company that has expressed concern, and the vast majority of the American business community view this as a very important service."

But Delta has a formidable ally: House Majority Leader Eric Cantor, a Virginia Republican who has called for winding down the bank's powers. His aides say he views the bank's activities as improper government interference into the private marketplace, putting taxpayers at risk. The U.S. government is ultimately on the hook for bank losses, though the bank consistently earns profits that are returned to U.S. taxpayers.

"Leader Cantor's position on the Export-Import bank is based on the policy goal that we need to include taxpayer protections and reforms in any extension of the bank's authority," said Laena Fallon, a spokeswoman.

Senate Democrats have proposed a four-year reauthorization of the bank along with an increase in the cap on its financing activities to US$140 billion from US$100 billion. They plan to attach it to an unrelated bill that would aim to ease the regulatory burden on small businesses trying to raise capital.

Mr. Cantor has circulated an alternative plan to renew the bank's mandate only through June 2013 and increase the financing cap to just US$113 billion, while instructing the White House to begin negotiations with foreign trading partners to wind down export subsidies.

The fight highlights a complicated relationship between Boeing and one of its top customers, Delta, which announced last August it would spend between US$1.2 billion and US$1.4 billion by 2014 to purchase 100 Boeing 737-900ER aircraft.

Delta has the backing of the airline industry's main trade group, Airlines for America, for which Delta CEO Richard Anderson serves as chairman. The group says financing credits from the Export-Import Bank allow Boeing customers overseas to finance jets at an interest rate at up to half the cost of U.S. carriers. That amounts to an annual saving of roughly US$4 million and US$5 million on the purchase of a US$261 million Boeing 777 aircraft, the airline trade group has said. For an order of 100 jets, that could potentially mean US$500 million a year in savings.

Delta, along with Airlines for America, is suing the Export-Import bank over the Air India-Boeing transaction, although the case isn't expected to affect the outcome of that sale.

Neither of Delta's main U.S. rivals United Continental Holdings Inc. or AMR Corp, owner of American Airlines, are involved in either the law suit or are backing its lobbying efforts.

U.S. companies that buy planes and other goods don't have access to assistance from the U.S. Export-Import Bank, but they often turn to similar institutions in other countries. Delta acknowledges that it benefits from export financing when it purchases airplanes from Canada's Bombardier Inc. or Brazil's Embraer S.A.

Delta General Counsel Ben Hirst said the two companies only sold planes with export financing attached, and that Delta would "be very happy if the Canadians and Brazilians got out of this business as well."

Companies like Boeing argue that the U.S. subsidies are needed to put them on par with foreign competitors, including Airbus, a unit of European Aeronautic Defence & Space Co., that receive similar assistance from their home countries.

Boeing said in a statement that the bank is "vital to helping level the playing field" globally. The bank also pointed out that the U.S. and other countries agreed to changes to export financing in 2010 that go into effect next year. "If in the process of reauthorizing the Bank the United States makes changes on its own to export credit terms agreed to in that process, the U.S. would effectively unilaterally disarm, while our overseas competitors would continue to support their industries," the company said.

Mr. Cantor's approach is backed by the Republican Study Committee, a large group of conservative House Republicans that now accounts for the majority of the GOP's House lawmakers.

During a visit to a Boeing plant in Everett, Wash., last month, President Obama said the bank has enabled companies like Boeing to expand in emerging markets and compete with overseas companies that receive subsidies. "I will go anywhere in the world to open up new markets for American products," he said, later adding: "We've got to make sure we're making it easier for companies like Boeing to create jobs here at home and sell our products abroad."