NEW ORLEANS -- BP allayed last-minute government fears of making the disaster worse and began testing the new, tighter-fitting cap Wednesday that could finally choke off the oil leak in the Gulf of Mexico.
Retired Coast Guard Adm. Thad Allen, the Obama admininistration's point man on the disaster, said the government gave the go-ahead after carefully reviewing the risks.
''What we didn't want to do is compound that problem by making an irreversible mistake,'' he said at the end of a 24-hour roller-coaster of hopes raised, hopes dashed and hopes raised again along the Gulf Coast.
The cap -- a 75-ton metal stack of pipes and valves -- was lowered onto the well on Monday in hopes of either bottling up the oil inside the well machinery, or capturing it and funneling it to the surface. But before BP could test the equipment, the government intervened because of second thoughts about whether the buildup of pressure from the gushing oil could rupture the walls of the well and make the leak worse.
''We sat long and hard about delaying the tests,'' Allen said. He said that the pause was necessary in the interest of the public, the environment and safety, and that officials were convinced the test could go forward.
The test began with BP shutting off pipes that were funneling some of the oil to ships on the surface so the full force of the gusher went up into the cap. Then deep-sea robots began slowly closing, one at a time, three openings in the cap that let oil pass through. Ultimately, the flow of crude will be blocked entirely. All along, engineers will be watching pressure readings to learn whether the well is intact.
Allen said BP will monitor the results every six hours and end the test after 48 hours to evaluate the findings.
The one-day delay came just when it looked as if the Gulf oil crisis was nearing an end. The holdup was met with disappointment along the Gulf Coast.
''This thing's been going on for so long now, it's time to take a gamble,'' said Mitch Jurisich, a third-generation oyster farmer from Empire, La. ''If it's going to blow the bottom of the ocean out, it's just going to blow the bottom out.''
White House spokesman Robert Gibbs said the government acted ''out of an abundance of caution to do no harm,'' and added that he did not consider the delay to be ''some giant setback.''
BP stock was down more than 2 percent in afternoon trading in London on news of the delay after recouping some of its losses earlier this week when the cap project seemed to be moving ahead.
With the testing on hold, oil continued to spew nearly unimpeded into the water. Two vessels on the surface collected about 700,000 gallons on Tuesday, BP said. The government estimates 1.5 million to 2.5 million gallons are leaking every day.