* BP ready with containment cap
* Cap should capture majority of oil, not all
* Relief well best option, but two months away (Recasts with top kill failure)
By Kristen Hays
HOUSTON, May 29 (Reuters) - BP Plc (BP.L) (BP.N) gave up on its failed "top kill" effort to smother a Gulf of Mexico oil leak on Saturday and focused on a plan to cap a piece of equipment at the wellhead and corral spewing oil and gas.
"We do think it will capture the majority of the oil if it works. We can't guarantee that," BP Chief Operating Officer Doug Suttles said of the next step at a daily briefing on Saturday with the U.S. Coast Guard. He said it could take four days or longer to show results.
Suttles said the top kill, or the pumping of heavy fluids and materials into a failed blowout preventer to quell the leak in the well, did not stop the flow of oil and gas into the Gulf.
Although Chief Executive Tony Hayward said on Friday that BP would not know until Sunday whether the top kill was a success or failure, Suttles said company and government officials decided on Saturday to give it up and move on.
"It was an option we felt was best to pursue based on the information we had," he said. "Obviously we didn't know."
Hayward said in a statement that he was disappointed that the top kill failed, but BP is ready to move immediately to the containment cap.
"Based on what we know now, we believe the containment cap is the most effective way to minimize the impact of the oil leak on the Gulf ecosystem and the people of the region," Hayward said.
Coast Guard Admiral Mary Landry, who spoke at the briefing alongside Suttles, said the only certain solution is a relief well that is being drilled to intercept and plug the leaking well far beneath the seabed.
The other efforts haven't been tried a mile (1.6 km) beneath the water's surface, where only underwater robots can tolerate the extreme pressures and temperatures.
Suttles said BP has tried to keep increasingly skeptical officials and the public informed of the progress of its efforts to plug the well.
"I can also say this scares everybody. The fact that we can't make this well stop flowing, or we haven't succeeded in that so far," he said.
The containment cap is the next effort to quell the leak, which was discovered after Transocean Ltd's (RIG.N) Deepwater Horizon rig exploded on April 20, killing 11 workers. BP owns the well.
BP's plan is to saw off a bent pipe on top of a lower marine riser package, or LMRP, that sits atop a failed blowout preventer at the wellhead.
That pipe was connected to the rig, and the two leaks are spewing from it.
The cap with a grommet seal will cover the opening left when the pipe is sawed off. Captured oil and gas would be channeled through a pipe that connects the cap to a drillship, where it would be stored.
"We haven't done it to this date because we needed the diagnostic data to make sure we didn't make the situation worse," Suttles said at a news conference earlier on Saturday.
Suttles said the company also is preparing to place a working blowout preventer on top of the failed one if the cap option fizzles.
Drilling continues on a relief well intended to intercept the leaking well and plug it far beneath the seabed. BP expects the first well to be finished by late July or early August. (Additional reporting by Ed Stoddard in Fourchon Beach, Louisiana; editing by Mary Milliken and Mohammad Zargham)