HOUSTON (Reuters) - BP Plc started sawing extraneous pipes on Tuesday at the seabed site of its latest attempt to corral oil leaking from a ruptured well in the Gulf of Mexico.

Moving past its failed “top kill” attempt to plug the leak, BP focused on containment rather than stopping the flow.

“We’re not talking about capping the well anymore. We’re talking about containing the well,” Coast Guard Admiral Thad Allen said at a news conference on Tuesday.

BP is counting on a pair of relief wells being drilled to intercept and plug the leak far beneath the seabed.

But the relief wells, each begun in May, will not be finished until early to mid-August -- forcing the company to keep seeking a stopgap.

This week BP aims to place a containment cap with a grommet seal at the bottom on top of a lower marine riser package, or LMRP, that sits atop a failed blowout preventer at the seabed.

If the cap and seal work as hoped, leaking oil and gas will be channeled through a pipe that connects the cap to a drillship a mile above the seafloor.

In addition, BP is planning to back up the containment cap operation by using seabed equipment installed for the failed top kill to pull oil and gas from the well and channel it to a different vessel at the water’s surface.

BP expects that system to be ready by mid-June.

The company also is planning a containment system that can be interrupted if a hurricane blows through the Gulf. The 2010 Atlantic hurricane season began on Tuesday, and forecasters expect it to be active.

That would involve a riser that hangs 300 feet below the water’s surface, and can connect to a hose attached to the containment cap.

If a storm approaches, the hose can be disconnected so the drillship can move out of the way, BP spokesman Jon Pack said.

The company has consistently said it expects up to a fifth of the leaking oil to escape the cap and seal.

SAW AND SHEAR

Pack said that a diamond saw held by one of several underwater robots at the seabed on Tuesday was removing pipes next to a larger, broken pipe -- called a riser -- from which up to 19,000 barrels (800,000 gallons/3 million liters) of oil are leaking into the Gulf daily for the sixth consecutive week.

At times, the sawing could be seen on BP’s live seabed wecbam feed.

The riser bent and broke as Transocean’s Deepwater Horizon drilling rig exploded and sank in April, killing 11 workers.

Once the smaller pipes are gone, the robots will use huge shears to slice off the riser.

Then the saw will shave jagged bits to create an even opening for the cap.

Pack said oil and gas would “very definitely” spew from the opening during the operation. U.S. scientists said the move could temporarily increase the flow by 20 percent.

White House adviser Carol Browner called the possibility that the flow will temporarily increase “deeply, deeply troubling.”

BP said the cap is expected to be deployed later this week.

The cap is similar in theory to a much larger containment dome that BP tried to place over the end of the broken riser in early May. Cold seawater filled the dome and mixed with natural gas at high pressure, forming a type of ice that blocked oil from flowing upward.

Pack said the smaller containment cap is designed to keep seawater out and avoid that problem.

Analysts are skeptical of the cap plan.

Given previous failures, “this new prospect does not give us any real confidence that it will succeed,” analysts from British firm Arbuthnot Research said in a note to clients.