An administration official, who asked not to be identified because of the sensitivity of the talks with BP, said the government was acting out of "abundance of caution," adding that until BP answers the questions the government is reluctant to move forward.
The development was a setback for BP, which seemed be on track to place a temporary cap on the well following nearly three months of failed attempts to stop the spill, which has sullied beaches from Florida to Texas.
Special Section: Disaster in the Gulf
Now it has halted the cap replacement, needed tests, and the drilling of two relief wells considered the ultimate solution to the gusher.
BP was vague about the reasons for pushing back tests and for halting the relief wells, suggesting unspecified concerns before pointing to the government.
Kent Wells, a senior vice president at the oil giant, said at a morning news briefing that it was the government's call late Tuesday to re-evaluate plans for testing the new cap over the leak. That plan was put on hold for 24 hours.
With oil still gushing freely into the Gulf, Wells said BP and federal officials will re-evaluate the best path forward after the 24 hours.
But he did not commit with certainty to returning to the plan, in place before the late Tuesday delay, to shut the leak off by closing the valves on the new cap. Wells suggested other oil collection options might be redeployed.
"We want to move forward with this as soon as we are ready to do it," he said.
The capping procedure consists of closing off two of the containment cap's three valves to trap new leaking oil inside, reports CBS News correspondent Mark Strassman.
Next, a robotic arm would slowly close the final valve called a choke line, theoretically sealing in all the oil.
If sensors show a high pressure reading - 8,000 to 9,000 pounds per square inch - that means the well is strong and containment can continue. But lower readings - PSI between 4,000 and 5,000 - could mean the well's hidden soft spots are letting oil escape, reports Strassman.
As of Wednesday, the 85th day of the disaster, between 92 million and 182 million gallons of oil had spewed into the Gulf.
Along the Gulf Coast, where the spill has heavily damaged the region's vital tourism and fishing industries, people anxiously awaited the outcome of the painstakingly slow work.
"I don't know what's taking them so long. I just hope they take care of it," said Lanette Eder, a vacationing school nutritionist from Hoschton, Ga., who was walking on the white sand at Pensacola Beach, Fla.
"I can't say that I'm optimistic - It's been, what, 84 days now? - but I'm hopeful," said Nancy LaNasa, 56, who runs a yoga center in Pensacola.
In the meantime, oil continued spewing into the Gulf.