Al-Bashir said it was still unclear whether the African Union, which has 7,000 under-financed troops in Darfur, would retain total control of the force.
He also said the UN support contingent must have field personnel "with ranks below that of the military commander."
Ban has already agreed that the commander would be an African.Peace agreement
Most of the objections in the three-page letter are based on provisions in the Darfur Peace Agreement (DPA), which was signed last May between one rebel group and the Khartoum government.
"Proposals that tend to amend, nullify or suspend any article of the DPA will not be acceptable as it may reopen discussions over issues that were previously settled without difficulty," he said.
"The Darfur peace agreement is the framework and reference upon which the United Nations should ... deliver its proposed support packages," Bashir said in the letter."
But the process has moved on since the DPA agreement, the UN and Sudan reached a deal in Addis Ababa on November 16 that was endorsed by Sudanese officials at an African Union meeting in Abuja, Nigeria, two weeks later.Political process
Marie Okabe, a UN spokeswoman, said Sudan's letter, which arrived on Thursday, "contains some positive elements, including a strong expression of support for the joint African Union-UN efforts to re-energise the political process and some assurances with regard to humanitarian assistance to the people of Darfur."
"But it also contains some elements which seem to challenge the agreement reached last November in Addis Ababa and Abuja on peacekeeping in Darfur," she added.
The Security Council, which has expressed frustration with Sudan's delay in answering Ban's letter, intends to discuss the issue next week.
Fighting in Darfur began in February 2003 when men from non-Arab tribes tribes took up arms, complaining of decades of neglect and discrimination by the Arab-dominated Khartoum government.
The United Nations and humanitarian groups accuse the government of arming Arab militia, known as the Janjawid, notorious for killing and raping civilians and looting and burning down their homes.
At least 200,000 people in the region have died, four million need emergency aid and 2.5 million are living in makeshift camps.