* Top kill making progress, success not yet known
* CEO: leak wrestled to ground, no bullet in head yet
* Effort to continue as BP prepares for two other options (Adds comment from briefing)
By Kristen Hays
HOUSTON, May 28 (Reuters) - BP Plc's (BP.L) critical "top kill" is making progress beating back an oil leak in the Gulf of Mexico, but the job is not finished, Chief Executive Tony Hayward told Reuters during an inspection of the spill in a helicopter.
"We have wrestled it to the ground but we haven't put a bullet in its head yet," Hayward said.
He also said the effort's chances of success remained at 60-70 percent, giving it better odds than analysts who gave it 50/50 odds.
Hayward said earlier on Friday that the company can't call it a success or failure until Sunday.
Hayward said in a series of television interviews that the procedure, which began on Wednesday afternoon, was operating "according to plan" and it would be another 48 hours before BP had "a conclusive view."
"We don't know whether we will be able to overcome the well," he told NBC's "Today" show.
Before the top kill started on Wednesday, BP said it would take between half a day and two days -- or Friday at the latest -- to gauge its success. Thursday the company said it could take another 24 hours or more, and on Friday Hayward pushed the time to Sunday.
Later on Friday, Chief Operating Officer Doug Suttles insisted BP had no set timeline for the procedure, but he acknowledged that the company cannot continue indefinitely until a relief well is drilled to permanently cap the leaking well. The company expects to finish drilling that well by early August.
"We'll continue this operation as long as necessary until we're successful with it or until we're convinced it won't succeed," Suttles told a news briefing.
The well has been leaking thousands of barrels of oil each day for five weeks, after a blowout preventer at the seabed failed and Transocean Ltd's (RIG.N) Deepwater Horizon drilling rig exploded and sank, killing 11 workers.
Analysts say the top kill is increasingly seen as being at a crucial juncture as oil has invaded some of Louisiana's delicate marshlands and threatens much of the U.S. Gulf Coast.
"If the top kill hasn't fixed this by Monday, there are going to be lots of frustrated people (politicians, investors, U.S. citizens, etc.) and we'd expect the tension/anger level about the spill to dial up yet another notch," Houston energy investment and merchant bank Tudor Pickering Holt & Co. said in a research note.
The top kill involves pumping "drilling mud," or heavy fluids, into the blowout preventer so it will push the oil back down the well and stop the leak.
BP began pumping mud on Wednesday afternoon, then stopped overnight to analyze pressure readings. High pressure means oil is still leaking, while lower pressure indicates the mud is pushing it down.
Some mud went up instead of down and escaped from the larger leak at the end of a broken pipe and a smaller leak where the pipe is bent as it extends from the top of a piece of equipment atop the blowout preventer. BP couldn't say how much mud escaped.
THE JUNK SHOT
Hayward said that late on Thursday afternoon and into the night BP pumped a "junk shot" -- more solid materials like shredded rubber and golf balls -- into the blowout preventer to add heft.
"We have some indications of partial bridging which is good news," Hayward told CNN on Friday.
Hayward said BP would resume pumping mud on Friday, but Suttles dodged the question when asked during the briefing if pumping had restarted.
"At times we will pump, at other times we will monitor, at times we will use these other materials to block the flow," he said.
BP has said the last step of the kill will be to pump cement into the well to plug the leak.
If the top kill fails, BP has two more options on tap.
First, it would cut the bent pipe from the lower marine riser package, or LMRP, atop the blowout preventer and place a cap over the opening. The cap would be connected to a pipe that would transport "most" of the oil to a drill ship at the water's surface, BP said in a statement on Friday.
The LMRP cap is already at the seabed near the blowout preventer, BP said.
Second, BP can place a second blowout preventer atop the failed one, the company said.
Drilling began on two relief wells earlier this month, each a half-mile (800 meters) from the leaking well, intended to intercept and cap it far beneath the seabed.
However, Transocean Chief Executive Steven Newman said on Friday that drilling was suspended on one of the wells while the top kill is ongoing.
BP spokesman David Nicholas said it stopped in preparation for the possible placement of the second blowout preventer atop the failed one.
Each rig has its own blowout preventer, and the rig that was suspended was using it at the seabed while drilling the second relief well. The operation stopped so that the blowout preventer can be available to BP if the company decides to use it to try to stop the leak, Nicholas said.