ON THE GULF OF MEXICO – Top hats and junk shots are on the list of possible next steps as BP, casting about after a 100-ton containment box failed, settles in for a long fight to stop its uncontrolled oil gusher a mile under the Gulf of Mexico.

As engineers at BP PLC were wrestling with a shopping list of ways to plug the well or siphon off the spewing crude, BP's chief executive Tony Hayward said Monday that the company will deploy a dome, or so-called top hat, to plug the leak.  The dome would be smaller than the 100-ton containment box that failed last week, Hayward told reporters.  

Meanwhile, BP also began spraying chemical dispersants underwater at the main oil leak site on Monday. 

BP PLC spokesman Mark Proegler said the company received Environmental Protection Agency approval and began pumping dispersant on the site starting at 4:30 a.m. Monday. The company plans to continue spraying and taking tests. The dispersants had never been tried at such depths before this spill and officials have been worried about the effect on the environment.

"There's a lot of techniques available to us. The challenge with all of them is, as you said, they haven't been done in 5,000 feet of water," BP Chief Operating Officer Doug Suttles told NBC's "Today" show Monday.

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The cold, pitch-black depth of the seafloor is a formidable problem. That's where icy slush formed inside a four-story container and foiled plans to funnel the oil to a surface tanker, which had been the best hope for containing the leak quickly while a drill rig spends up to three months boring a new well to shut down the old one permanently.

By Monday morning, the boat that had lowered the containment box had moved five or six miles from the site of the oil leak to a staging area. It was unclear if the boat had taken the large box with it or left it on the seafloor.

The engineers appear to be "trying anything people can think of" to stop the leak, said Ed Overton, a LSU professor of environmental studies.

On land, helicopters were expected to drop sandbags in Louisiana to guard against thick blobs of crude that began washing up on beaches as the well spills at least 200,000 gallons of oil a day into the Gulf.

On Sunday, in a waterfront yard in Port Fourchon, La., a tractor-trailer dumped a load of sand, which workers planned to pack into 5-cubic-yard bags. Once the bags are ready, the Army National Guard will airlift them on Monday to five spots along a four-mile stretch of coastline between Port Fourchon and the Jefferson Parish line, said Lafourche Parish compliance officer Robert Passman.

"We want to block it off to where the oil doesn't get into the marsh areas," said Passman. "What they're trying to do is just prevent. I know it's still east of here but they're just trying to do a little prevention."

BP — which is responsible for the cleanup — said Monday the spill has cost it $350 million so far for immediate response, containment efforts, commitments to the Gulf Coast states, and settlements and federal costs. The company did not speculate on the final bill, which most analysts expect to run into tens of billions of dollars.

Among plans under consideration for the gusher, BP is looking at cutting the riser pipe, which extends from the well, undersea and using larger piping to bring the gushing oil to a drill ship on the surface, a tactic considered difficult and less desirable because it will increase the flow of oil.

A junk shot would be followed by cement to seal the leak and the technique is something company officials said they might try next week. The smaller container could be tried first, around the middle of this week.

An estimated 3.5 million gallons of oil have spilled since an explosion on April 20 on the drilling rig, the Deepwater Horizon, 50 miles off the Louisiana coast. At that pace, the spill would surpass the 11 million gallons spilled in the Exxon Valdez disaster by next month.

Above the oil leak, waves of dark brown and black sludge crashed into the support ship Joe Griffin. The fumes there were so intense that a crew member and an AP photographer on board had to wear respirators while on deck.

Philip Johnson, a petroleum engineering professor at the University of Alabama, said cutting the riser pipe and slipping a larger pipe over the cut end could conceivably divert the flow of oil to the surface.

"That's a very tempting option," he said. "The risk is when you cut the pipe, the flow is going to increase. ... That's a scary option, but there's still a reasonable chance they could pull this off."

Johnson was less optimistic that a smaller containment box would be less susceptible to being clogged by icelike crystals.

"My suspicion is that it's likely to freeze up anyway," he said. "But I think they should be trying everything they can."

There was a renewed sense of urgency as dime- to golfball-sized balls of tar washed up Saturday on Dauphin Island, three miles off the Alabama mainland at the mouth of Mobile Bay and much farther east than the thin, rainbow sheens that have arrived sporadically in the Louisiana marshes. Until Saturday none of the thick sludge — those indelible images from the Valdez and other spills — had reached shore.

The containment box plan had been designed to siphon up to 85 percent of the leaking oil to a tanker at the surface. It had taken about two weeks to build it and three days to cart it 50 miles out and slowly lower it to the well.

Icelike hydrates, a slushy mixture of gas and water, clogged the opening in the top of the peaked box like sand in a funnel, only upside-down.

The blowout aboard the rig, which was being leased by BP, was triggered by a bubble of methane gas that escaped from the well and shot up the drill column, expanding quickly as it burst through several seals and barriers before exploding, according to interviews with rig workers conducted during BP's internal investigation. Deep sea oil drillers often encounter pockets of methane crystals as they dig into the earth.

Lane Zirlott, 32, a commercial fisherman from Irvington, Ala., said he's not frustrated about BP failing so far to cap the leak because he understands how difficult the job is.

"When they said they were going to put this little cap over this thing, I laughed and said there's no way," he said. "I said there's no way they're going to do that. And then sure enough, it didn't happen."

The Associated Press contributed to this report