They also said he has back-tracked on agreements regarding Darfur in the pas, and that the letter leaves the size and command of a hybrid AU-UN force that would be deployed as the third step unresolved.
Al-Bashir's letter was a response to several phone calls with Annan and a letter from the secretary-general delivered by a personal envoy, Ahmedou Ould Abdallah.
He is expected to brief the council on Wednesday afternoon at a meeting which Annan will also attend, UN officials said.
Al-Bashir rejected a Security Council resolution adopted in August that called for more than 20,000 UN peacekeepers to replace the overwhelmed AU force in Darfur, and had opposed deployment of UN troops in a hybrid force.
He claims a UN force would compromise Sudan's sovereignty and try to recolonise the country. In the letter to Annan, al-Bashir dropped his opposition to the hybrid force.
He said the conclusions of a November 16 meeting of key Sudanese and international diplomats in Addis Ababa, Ethiopia, and the November 30 summit of the AU's Peace and Security Council in Abuja, Nigeria, which endorsed the three-step UN plan, "constitute a viable framework for peaceful settlement to the conflict in Darfur".
Al-Bashir said Sudan agrees that implementation of the first two phases of the UN support package for Darfur should start "as scheduled".
The first phase would add 105 military officers, 33 UN police, 48 international staffers, 36 armoured personnel carriers, night-vision goggles, and Global Positioning equipment to the African Union force, according to a UN report last month.
A second, larger support package would include the deployment of several hundred UN military, police and civilian personnel to the African Union mission along with substantial aviation and logistical assets.