ATLANTA — The ultimate sealing of BP’s Gulf oil well may not get under way until late this month or early October because experts want more time to analyze the well, fish out a broken pipe and possibly apply another cement seal on the top for “”more insurance”” against unlikely troubles, a top federal official said.

National Incident Commander Thad Allen, in his conference call with reporters Wednesday, reiterated his promise that there is “”no threat”” of oil leaks from the well now that a new, stronger blowout preventer has been placed on top of it.

The new equipment gives experts the luxury of taking a few extra steps to ensure that they will not encounter problems with the final “”bottom kill.”” During this procedure, the original well’s outer ring, or annulus, will be intersected underground with a relief well and pumped with mud and cement.

The drilling of the relief well’s final 50 feet was supposed to begin this week. But Allen said that crews want to conduct further diagnostics on the well and make a few more attempts to yank out a 3,500-foot piece of pipe from the original drilling operation that is assumed to be lodged inside. Earlier attempts to remove the pipe in late August were unsuccessful.

Depending on the amount of testing, the sealing process could begin about Sept. 18 or Sept. 28 and take about a week, Allen said.

Darryl Bourgoyne, director of the petroleum engineering research lab at Louisiana State University, said that the broken pipe, if recovered, may provide some clues as to why the original blowout preventer failed to close up the well the night of April 20, when a fiery blowout killed 11 men and eventually sank the Deepwater Horizon rig off the Louisiana coast.

One theory is that the pipe got jammed in the blowout preventer’s shear ram — the well’s last line of defense — and kept it from closing properly. Bourgoyne said that by clearing the well of the broken pipe, crews may also be able to gain better access for measuring devices that could better assess the condition of the well — and better prepare engineers for the bottom kill.

Crews were able to close up the well in early August by pouring mud and cement into the top, but the bottom kill has long been touted as the ultimate solution for a wild well that spewed an estimated 4.9 million barrels of oil into the Gulf of Mexico.