Among the concerns was that if the well was damaged during the test, oil and gas might leak from the seafloor around the well rather than up through the well bore as it is now.

Earlier, Kent Wells, a senior vice president for BP, said the test procedures were being reviewed to make sure scientists and engineers could interpret them properly. “We don’t want to end up with a test with inconclusive results,” Mr. Wells said in a morning briefing from Houston.

He also announced that drilling of a relief well  considered the ultimate solution to stopping the gusher at its source  would be halted during the test as a precaution. The suspension of work would set the task back by a couple of days, he said.

Earlier in the week, BP officials had said that if the test showed that the well could hold pressure, the valves might remain closed. That would end the gusher that began shortly after the Deepwater Horizon drilling rig exploded April 20, killing 11 workers.

If the test shows the well is damaged, the flow of oil into the sea could still be stopped by increased collection of oil, a process that could continue for weeks, awaiting completion of a relief well.

Admiral Allen said the government had asked BP for more information on the structural strength of the well. And in allowing the test to proceed, the government stipulated that pressure be allowed to build up in intervals, with acoustic tests to gauge the well’s condition every six hours. That would most likely lengthen the duration of the test, which had been expected to last from 6 to 48 hours.

But the admiral said that the well would be monitored closely during the first three hours and that the test could be even shorter if the pressure stays low. The test brings to an end, at least temporarily, a period when more oil had been spewing from the well after a loose-fitting cap was removed to begin work on the new one. The old cap was diverting about 15,000 barrels of oil a day.