* Amount of oil leaking unchanged since top kill started

* BP preparing for next effort to cap Gulf of Mexico well (Adds quotes, details)

FOURCHON BEACH, La./HOUSTON, May 29 (Reuters) - BP Plc's BP.LBP.N "top kill" has not stopped a Gulf of Mexico oil leak and the company is assessing whether to continue or move on to something else, BP Chief Operating Officer Doug Suttles said on Saturday.

“I don’t think the amount of oil coming out has changed,” he said at a news conference at Fourchon Beach, Louisiana, about 72 hours after the effort began on Wednesday. “Just by watching it, we don’t believe it’s changed.”

A live feed of the leak, available on BP’s website, showed preparations Saturday morning for BP’s next step. An underwater robot gripped a saw near the leaking pipe atop a failed blowout preventer.

BP’s next option is to slice off the pipe and place a cap over the opening. As the camera moved around, the live feed later showed thick plumes coming from both leaks.

The cap operation is known as the lower marine riser package cap, and Suttles confirmed that BP had been preparing for that step “all along.”

“If we have to go to it, we can do it as quickly as possible,” he said.

BP has said previously the company was “planning in parallel,” or getting ready for other options while working on the top kill -- the injection of heavy drilling fluid and solid materials, like shredded rubber and golf balls, into the blowout preventer to try to push oil and gas back down the well.

Suttles stopped short of saying the top kill has failed. “We’ve said all along this may or may not be successful,” he said.

Suttles will give another update at a daily briefing, scheduled for 6 p.m. CDT (2300 GMT), a BP spokesman said.

Suttles also said the company believes oil and gas are being smothered when BP is pumping fluids and materials “at a high rate” into the well.

RELIEF WELL TWO MONTHS AWAY

The top kill is BP's latest effort to quell the leak, which was discovered after Transocean Ltd's RIG.N Deepwater Horizon rig exploded on April 20, killing 11 workers.

Since Wednesday, BP has periodically pumped fluids and materials, and monitored pressure between pumpings. Suttles has said higher pressure indicates the leak is unchecked, while lower pressure indicates progress in beating back the leak.

If the cap option proceeds, once the bent pipe is cut off the lower marine riser package, a containment cap and seal would be placed on the opening. 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 on Saturday.

He said the company was also preparing to place a working blowout preventer on top of the failed one if the cap option fizzles.

Drilling continues on one of two planned relief wells 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. (Editing by Mary Milliken and Mohammad Zargham)