NEW ORLEANS (AP) - BP robots attached a new, tighter-fitting cap on top of the gushing Gulf of Mexico oil leak Monday, raising hopes that the crude could be kept from polluting the water for the first time in nearly three months.

Placing the cap on top of the leak was the climax of two days of delicate preparation work and a day of slowly lowering it into position a mile below the sea. The capping project - akin to building an underwater Lego tower - is just a temporary fix, but the oil giant's best hope for containing the spill.

The next unknown is whether the 18-foot-high, 150,000-pound metal stack of pipes and valves will work. BP plans to start tests today, gradually shutting the valves to see if the oil stops or if it starts leaking from another part of the well.

Residents have been skeptical BP can deliver on its promise to control the spill, but the news was still welcome on the coast. Dwayne Touchet, a 44-year-old shrimper from Welsh, La., said he was relieved to hear the cap was on and can only pray that it works. Touchet is working in the Vessels of Opportunity program, where BP employs local boat owners and fisherman out of work because of the spill.

"It's not over, there's still a lot of oil to clean up. We don't know how it will affect it (the water) in the years to come, all we can do is trust in the Lord," he said.

Around 6:30 p.m. CDT, live video streams trained on the wellhead showed the cap being slowly lowered into place, 11 hours after BP Chief Operating Officer Doug Suttles said the company was close to putting the seal in place. BP officials said the device was attached around 7 p.m.

The cap will be tested and monitored to see if it can withstand pressure from oil and gas starting Tuesday morning for six to 48 hours, according to National Incident Commander Thad Allen.