The assessment for increasing the troop strength to 12,300 was to be presented to the AU Peace and Security Council when it meets on Thursday in Addis Ababa to discuss the situation in Darfur.
The AU force now in Darfur is "extremely stretched" and cannot fulfil its mandate, said the assessment done in March by staff based in the Sudanese capital, Khartoum, and from the organisation's headquarters in the Ethiopian capital.
The report said troop numbers must initially be increased to 5887, in addition to 1560 civilian police, by August, before considering a much larger deployment.
If the Sudanese government "remains unable to provide appropriate levels of security to support the return of internally displaced persons and the delivery of humanitarian assistance in all parts of Darfur, consideration has been given to ... increase the force to approximately 12,300," the assessment said.
The African Union currently has 2200 troops in Darfur out of an initial proposal of 3320.
The conflict in Darfur has brought
immense misery to many
"Militarily, the force should be in a position to promote a secure environment across Darfur," the report said.
In Brussels, Nato allies agreed on Wednesday to consider providing logistical help to the AU's force in Darfur. The agreement followed a written request from the chairman of the AU Commission, Alpha Oumar Konare, said Nato spokesman James Appathurai.
The Darfur conflict surged in February 2003 after rebel tribes took up arms, complaining of discrimination by the government in Khartoum. The government is accused of responding by backing a scorched-earth counter-insurgency by pro-government militias.
War-induced hunger and disease have killed more than 180,000 people, according to UN estimates. At least 2 million have been made homeless by the conflict. No firm estimates of the number killed in fighting exists.
UN Secretary-General Kofi Annan has said it is possible that UN peacekeepers could complement AU troops in Darfur. His special envoy to Sudan, Jan Pronk, has said 8000 troops are needed for Darfur.