WASHINGTON — The Obama administration failed to act upon or fully inform the public of its own worst-case estimates of the amount of oil gushing from the blown-out BP well, slowing response efforts and keeping the American people in the dark for weeks about the size of the disaster, according to preliminary reports from the presidential commission investigating the accident.

The government repeatedly underestimated how much oil was flowing into the Gulf of Mexico and how much was left after the well was capped in July, leading to a loss of faith in the government’s ability to handle the spill and a continuing breach between the federal authorities and state and local officials, the commission staff members found in a series of four reports issued Wednesday.

“By initially underestimating the amount of oil flow and then, at the end of the summer, appearing to underestimate the amount of oil remaining in the gulf,” one of the reports stated, “the federal government created the impression that it was either not fully competent to handle the spill or not fully candid with the American people about the scope of the problem.”

The reports also say that about two weeks after the BP rig exploded, the National Oceanic and Atmospheric Administration asked the White House for permission to make public its worst-case models for the accident. The White House Office of Management and Budget initially denied the request, according to government officials interviewed by the commission’s staff members.