The Army Corps of Engineers announced Friday the signing of a $6 million contract with two North Carolina firms to build the Little Dell Dam.

Sens. Jake Garn and Orrin Hatch, both R-Utah, were informed that Summit Brothers Co. and J.E. Sterns Co., of Hickory, N.C., would build the dam under a contract calling for completion by Sept. 30, 1991.Little Dell has been in the planning stage for more than 30 years, until money was appropriated for it in 1988.

The Air Force also awarded a $152 million contract with Hercules Inc. for 24 MX missile third stage engines and five test engines for the rail-garrison MX "Peacekeeper" force. The service cleared $126.5 million of the work this week. The engines will be produced in Magna.