Nigeria is so displeased with the performance of its 40 Soviet military advisers that it is asking most of them to leave, according to the Pentagon.

Defense officials said that they know of no blanket ejection notice yet issued to the Soviet team but acknowledged that all but five of the advisers are expected to be asked to leave during the next year.

One Nigerian complaint, according to defense officials, is that the Soviet Union has been slow in delivering the spare parts needed to keep Mig21 fighter planes flying.

Carter administration officials were buoyed by the reports of Nigerian disaffection with Soviet advisers. Nigeria is a major source of U.S. oil, as well as the pivotal nation in Africa.

At the same time Nigerian relations with the Soviet military cools, the U.S. Army Corps of Engineers is being warmly received as plans advance to help the African country tame the Niger River and develop inland waterways for commerce.

The Soviets' military ties with Nigeria date back to the 1960s, although the big arms agreement was made in 1974. The Mig21, then considered a hot fighter, was on the promised list.

U.S. officials said it was too early to tell whether Nigeria would follow Egypt's lead and turn to the United States to supply it with arms once Soviet military ties were broken.