CREATED IN 1934, the Export-Import Bank of the United States provides direct loans, loan guarantees and credit insurance to enable foreign purchases of U.S. products that private-sector banks might not finance. When trade credit dried up after the financial panic of 2008, Ex-Im’s lending soared from $14.4 billion in fiscal 2008 to $32.7 billion in fiscal 2011. As a result, the bank will hit its portfolio limit of $100 billion soon, perhaps before the agency’s legal mandate expires May 31.

A bipartisan Senate bill, supported by the Obama administration, would reauthorize Ex-Im through 2015 and increase its allowable portfolio to $140 billion. Backers say that Ex-Im sustains hundreds of thousands of jobs — while returning $1.9 billion in fees and interest to the Treasury in the past five years. But House Republicans are resisting, arguing that Ex-Im distorts markets and risks taxpayer money to aid big business.

Mere Tea Party ranting? Well, then-Sen. Barack Obama called Ex-Im “little more than a fund for corporate welfare” during his presidential campaign. He had a point: In fiscal 2011, more than half of Ex-Im’s loans and guarantees supported oil and gas or aerospace companies. For many years, Boeing has been Ex-Im’s leading customer.

Why can’t a blue-chip giant like Boeing sell planes without Washington’s help? Ex-Im supporters argue that even in normal economic times banks hesitate to extend long-term credit in emerging markets such as Vietnam and Colombia. Maybe so, but that contradicts another argument in favor of the bank — that it exposes taxpayers to little or no risk. Historically, Ex-Im’s default has been low — less than 2 percent. But it developed that record on the basis of a much smaller portfolio. To the extent that Ex-Im substitutes the U.S. government’s judgment for the market’s, it encourages emerging countries to over-invest in new aircraft and the United States to over-produce them. And that’s inherently risky.

What about job creation through export promotion, the rationale that converted Mr. Obama? Ex-Im surely creates jobs at Boeing, but whether it increases employment overall is another question. Delta Air Lines has complained, with justification, that Ex-Im-backed jet sales to competing airlines abroad put Delta at a disadvantage (though a new Ex-Im loan will help a Brazilian airliner send planes to Delta for maintenance). Nor does Ex-Im necessarily increase net exports. Currency fluctuations, tax rates and other competitive factors probably swamp Ex-Im’s impact; it backed a mere 2 percent of U.S. exports last year. And if not channeled to Ex-Im’s clientele, those resources might well have paid for other U.S.-made goods.

There is one hard-to-refute argument for Ex-Im: Everyone else does it. Europe and Japan have long subsidized big-ticket exports. In recent decades, the United States and other developed nations have negotiated mutual reductions in export subsidies — but now China, Brazil and India are getting into the act.

Probably the United States ought not to disarm unilaterally. But in the short term Congress should reform Ex-Im, by abolishing the well-intentioned but impractical requirement that it devote 10 percent of its resources to renewable energy exports and by ending the protectionist requirement that Ex-Im-financed goods travel on U.S.-flagged ships. In the medium term, the United States needs to lead a redoubled global diplomatic effort to phase out these market-distorting practices.