Senior managers complained oil giant BP was "taking shortcuts" by replacing heavy drilling fluid with saltwater in the well that blew out, triggering the massive oil spill in the Gulf of Mexico, according to witness statements obtained by The Associated Press.

Truitt Crawford, a roustabout for drilling rig owner Transocean LTD, told Coast Guard investigators about the complaints. The seawater, which would have provided less weight to contain surging pressure from the ocean depths, was being used to prepare for dropping a final blob of cement into the well.

"I overheard upper management talking saying that BP was taking shortcuts by displacing the well with saltwater instead of mud without sealing the well with cement plugs, this is why it blew out," Crawford said in his statement.

A spokesman for BP, which was leasing the rig Deepwater Horizon when it exploded April 20, killing 11 workers and triggering a massive oil spill in the Gulf of Mexico, declined to comment.

BP conducted tests Wednesday in preparation for its latest bid to plug the leaking well by force-feeding it heavy drilling mud and cement. BP Chief Executive Tony Hayward said on NBC's "Today" show that he would decide Wednesday morning whether to allow crews to try the procedure called a top kill.

Meanwhile, the statements from workers ahead of a hearing in New Orleans Wednesday and a congressional memo about a BP internal investigation of the blast indicated warning signs were ignored. Tests less than an hour before the well blew out found a buildup of pressure that was an "indicator of a very large abnormality," BP's investigator said, according to the congressional memo.

Still, the rig team was "satisfied" that another test was successful and resumed adding the seawater, said the memo by U.S. Reps. Henry Waxman and Bart Stupak to members of the Committee on Energy and Commerce, which is investigating what went wrong.

There were other signs of problems, including an unexpected loss of fluid from a pipe known as a riser five hours before the explosion, which the memo said could have indicated a leak in the blowout preventer, a huge piece of equipment that should have shut down the well in case of an emergency. BP has cited its failure as a contributor to the blast.

Frustration is growing with BP and the federal government as several efforts to stop the leak have failed. At least 7 million gallons of crude have spilled into the sea, fouling Louisiana's marshes and coating birds and other wildlife.

President Barack Obama prepared to head to the Gulf on Friday to review efforts to halt the oil that scientists said seems to be growing significantly darker, from what they can see in an underwater video. It suggests that heavier, more-polluting oil is spewing out.

Ahead of his trip, Obama planned to address an Interior Department review of offshore drilling that is expected to recommend tougher safety protocols and inspections for the industry, according to an administration official. The official spoke on condition of anonymity ahead of the public release Thursday of the findings of a 30-day review Obama ordered after the spill.

A new report from the Interior Department's acting inspector general alleged that drilling regulators have been so close to oil and gas companies they've been accepting gifts including hunting and fishing trips and even negotiating to go work for them.

The top kill BP is poised to try Wednesday involves pumping enough mud into the gusher to overcome the flow of the well.

Engineers plan to follow it up with cement that the company hopes will permanently seal the well. It may be several days before BP knows if it worked. Hayward earlier pegged its chances of success at 60 to 70 percent.

Bob Bea, an engineering professor at the University of California at Berkeley, said the procedure carries a high risk of failure because of the velocity at which the oil may be spewing.

"I certainly pray that it works, because if it doesn't there's this long waiting time" before BP can dig relief wells that would cut off the flow, Bea said.