Satellite Business Systems has ordered two satellites and related equipment worth $100 million from Hughes Aircraft Co.'s space and communications group.

The McLean-based communications company provides domestic U.S. telecommunications services ranging from integrated private networks for large organizations to discount long-distance telephone service for business and residential customers. SBS also provides international service through several foreign telecommunications administrations.

The satellites will operate in the Ku band--12 and 14 gigahertz (GHz). These are the same higher frequencies used by SBS' three satellites already in service and one other scheduled for launch in August 1984. All of the six SBS Hughes-made satellites are about seven feet in diameter and 21 feet tall when deployed in orbit.

The two new satellites, named SBS-5 and SBS-6, are scheduled for delivery in 1986. SBS-5 is expected to be launched by the space shuttle in late 1986. SBS-6 will be held as a spare until needed, perhaps as a replacement for SBS' first satellite, SBS-1, which was launched in November 1980 and has a seven-year design life, the company said.

The two new satellites have several improvements over their predecessors, including a 10-year life span and coverage of Alaska and Hawaii in addition to the continental 48 states.

SBS is jointly owned by Aetna Life & Casualty Co., Comsat and IBM Corp.