President Barack Obama, accompanied by National Incident Commander Adm. Thad Allen, makes a statement after being briefed on the BP oil spill relief efforts in the Gulf Coast region June 4 at Louis Armstrong International New Orleans Airport in Kenner, La.

Washington ? Weeks before the world had ever heard of the Deepwater Horizon oil rig, President Barack Obama stood in the Roosevelt Room of the White House poring over maps of oil drilling sites in the Gulf of Mexico, Alaska and elsewhere.

Satisfied that he knew all he needed to know and confident that it was safe, he decided to propose expanded offshore drilling.

“This is not a decision that I’ve made lightly,” he said when he unveiled his proposal on March 31.

“Oil rigs today generally don’t cause spills,” he added two days later. “They are technologically very advanced. Even during Katrina, the spills didn’t come from the oil rigs, they came from the refineries onshore.”

On April 20, the Deepwater Horizon rig exploded, setting off the largest oil spill in U.S. history. It drove Obama to freeze the proposal he’d just made.

An in-depth review by McClatchy Newspapers reveals how Obama reached that initial decision to expand offshore drilling — and why he failed to get information that might have led him instead to delay or oppose it and perhaps even raise questions about the deepwater drilling that was already under way.

Obama did roll back some of the offshore drilling that the George W. Bush administration had approved on Bush’s last day in office. However, Obama never challenged the Bush era’s fundamental faith in the oil industry or its ability to clean up a massive spill. Instead, he embraced expanded offshore drilling, in part to win Republican support for broader legislation to curb climate change.

“He deserved to be more skeptical,” said Stephen Hess, a veteran of four White Houses back to the Eisenhower administration and an expert on how presidents do their job.

“They hadn’t thought through the various ramifications. They should have, obviously. But it didn’t seem obvious at the time.”

“Not well thought through,” said Rick Steiner, a retired University of Alaska marine scientist. “If they had really done their job, they would have understood there was high risk here.”

Indeed, Obama and his team overlooked some important points as they prepared to give the green light to more offshore oil drilling. Expanding the drilling was something he’d promised to do during his campaign, when gas prices topped $4 a gallon, and it was a lure he planned to use to win Republican votes for legislation aimed at curbing climate change.

Among their oversights:

• Obama thought that funneling information through White House “czars” such as energy and environment adviser Carol Browner would get him all the data he needed.

• He failed to drill into the government bureaucracy to test that information. He didn’t, for example, ask about the Interior Department’s Minerals Management Service, which had prepared a report in 2000 on the dangers of deepwater drilling that proved to be eerily predictive of what happened in the Gulf. The MMS regulates offshore drilling.

• He never talked to the Coast Guard about its 2002 oil-spill drill in the Gulf or to the man who ran it, Adm. Thad Allen, who later would oversee the response to the Deepwater Horizon spill.

• He didn’t reach out to outside experts, such as the National Academy of Engineering, to question claims that deepwater drilling technology was dependable.

Top Obama administration officials say that they did an exhaustive job marshaling information for more than a year, and that the president asked what he needed to ask when it arrived at his desk. Anyone, they said, would grow complacent about the safety of offshore drilling after decades without a major spill.

“It’s really important to understand you have decades of nothing going wrong,” said one senior administration official, who spoke only on the condition of anonymity as a matter of White House policy.

“The last time you saw a spill of this magnitude in the Gulf, it was off the coast of Mexico in 1979,” a second senior administration official said. “If something doesn’t happen since 1979, you begin to take your eye off of that thing.”