The federal Minerals Management Service gave permission to BP and dozens of other oil companies to drill in the Gulf of Mexico without first getting required permits from another agency that assesses threats to endangered species — and despite strong warnings from that agency about the impact the drilling was likely to have on the gulf.

Those approvals, federal records show, include one for the well drilled by the Deepwater Horizon rig, which exploded on April 20, killing 11 workers and resulting in thousands of barrels of oil spilling into the gulf each day.

The Minerals Management Service, or M.M.S., also routinely overruled its staff biologists and engineers who raised concerns about the safety and the environmental impact of certain drilling proposals in the gulf and in Alaska, according to a half-dozen current and former agency scientists…

In a letter from September 2009, obtained by The New York Times, NOAA accused the minerals agency of a pattern of understating the likelihood and potential consequences of a major spill in the gulf and understating the frequency of spills that have already occurred there.