The findings and recommendations in the draft report await final approval by Gen. Thomas D. Waldhauser, the head of Africa Command.
A spokesman for Africa Command in Stuttgart did not return a request for comment on Friday.
The distance between military officials in Stuttgart and troops operating in African nations has long been a source of tension for American forces assigned to Africa Command. Mission planning is often complicated by bureaucratic hurdles that ground troops have navigated, in part by understating threats in their respective areas, so patrols can be organized and approved at lower levels.
Officials with knowledge of the investigative report say it describes a string of errors and bad decision-making that, together, may have led to last fall’s ambush outside the Nigerien village of Tongo Tongo. Fallout from the deaths threw the White House into crisis and prompted Congress to demand answers about what the soldiers were doing before the attack.
The draft report also details a breakdown in communications that may have stemmed from a failure by members of the American and Nigerien team, and their superiors, to check their equipment before heading out on the Oct. 4 mission.
As the unit came under attack, soldiers were unable to speak directly to French air support who flew out to help. Instead, the soldiers’ location coordinates were relayed through officers in Niamey, the capital, more than 100 miles away.
Senior Defense officials initially said that the investigation into the ambush, conducted by Maj. Gen. Roger L. Cloutier Jr., the Africa Command’s chief of staff, would be concluded by January. The report is now completed and has been circulating in the Pentagon, Defense Department officials said. But its public release has been delayed until after General Waldhauser appears before the Senate Armed Services Committee to present the command’s annual “posture hearing,” scheduled for the last week of February.
Defense officials said that the delay in part aims to keep senators from focusing on the Niger ambush during the hearing and, in turn, excoriating General Waldhauser when he testifies before the committee.
Military officials are preparing three separate versions of the report. A classified version will be shown to lawmakers and others with security clearances and a public version will be given to the news media. The third version will be given to the families of the four American soldiers who were killed.
Some current and former Pentagon policy officials and military commanders in Africa expressed skepticism about curtailing the training and advising missions in which American troops accompany local forces on ground patrols in West Africa.
“I’m not sure retreating from programs is the answer,” said Brian McKeon, a former top Pentagon policy official who visited Niger in 2015. “If we’re not going to do that kind of training, why are we there?”
Officials said that the scaling back of those missions, as called for in the report, would not apply to Libya or Somalia, where the United States has been engaging with local forces to fight the Islamic State and the militant group aligned with Al Qaeda known as the Shabab.
Brig. Gen. Donald C. Bolduc, who until last summer commanded United States Special Operations forces in Africa, said that at the time he left, American advisers were accompanying specially trained and equipped counterterrorism units in Tunisia, Cameroon and Niger.
The units, created about four years ago, train about 100 to 120 indigenous soldiers over roughly a two-year period. About a dozen American Special Forces are assigned to each unit, and the training costs “a few million dollars” to complete, General Bolduc said.
Accompanying the local soldiers on live training missions — up to just short of carrying out actual combat operations — is a key component and would be a mistake to curtail, General Bolduc said.
“They are a crucial program,” General Bolduc said in a telephone interview. “Those are our bread and butter.”
For almost a month, the Niger ambush was at the center of a political storm in Washington following the deaths of Staff Sgt. Jeremiah W. Johnson, Staff Sgt. Bryan C. Black, Staff Sgt. Dustin M. Wright and Sgt. La David T. Johnson.
Sergeant La David Johnson’s widow, Myeshia Johnson, said the president called her 12 days later and said her husband “knew what he signed up for,” even as Mr. Trump struggled to remember the slain soldier’s name. Representative Frederica S. Wilson, Democrat of Florida, who listened to Mr. Trump’s conversation with Ms. Johnson, criticized the president publicly for his words.
Mr. Trump angrily disputed that account and sent his chief of staff, John F. Kelly, to denounce Ms. Wilson to White House reporters. Mr. Kelly did so, but further flamed the controversy by mischaracterizing unrelated remarks by Ms. Wilson in 2015.
Video released by a local newspaper then showed Mr. Kelly’s portrayal to be false. Within days, the deaths of the four American soldiers in the remote West African semidesert had veered into the incendiary issue of race relations in the United States. Ms. Wilson is African-American, as is Myeshia Johnson and as was Sergeant La David Johnson.
Some Defense officials fear that the Pentagon report, when it is released, could reignite last year’s imbroglio.
There are roughly 6,000 American troops spread across Africa, the Pentagon said. This number can fluctuate for several reasons, including large training exercises and specific operations. Most of the forces, around 4,000, are at Camp Lemonnier, in Djibouti, the continent’s primary base of operations for Africa Command.
Countries in Africa where small teams of American Special Operations forces are deployed include Nigeria, Niger, Somalia, Libya, Mali, Chad and Mauritania.