WASHINGTON  A federal judge in New Orleans on Tuesday blocked a six-month moratorium on deep-water drilling projects that the Obama administration imposed after the massive oil spill in the Gulf of Mexico. The White House swiftly vowed to appeal the ruling.

In a 22-page opinion, the judge, Martin L. C. Feldman of United States District Court, issued a preliminary injunction against the enforcement of a late May order halting all offshore exploratory drilling in more than 500 feet of water.

Citing potential economic harm to businesses and workers, Judge Feldman wrote that the Obama administration had failed to justify the need for such “a blanket, generic, indeed punitive, moratorium” on deep-water oil and gas drilling.

“The blanket moratorium, with no parameters, seems to assume that because one rig failed and although no one yet fully knows why, all companies and rigs drilling new wells over 500 feet also universally present an imminent danger,” wrote Judge Feldman, a 1983 appointee of President Ronald Reagan. The administration’s order halted 33 exploratory drilling projects and suspended new permits, but did not affect platforms that were already in production.