Business Notes ROCKETS

Since President Reagan closed the space-shuttle program to most commercial cargo last summer, several U.S. aerospace firms have taken aim at the satellite-launching business. Last week McDonnell Douglas got a big boost in that race by snaring a $734 million Air Force contract for a fleet of up to 20 rockets to lift military satellites into orbit.

The contract means that the firm will not have to spend its own money to develop a rocket that can compete with Western Europe's Ariane program, which has a virtual monopoly on private satellite launches. McDonnell Douglas will also be able to go nose-to-nose with Martin Marietta, the maker of Titan-class rockets, which has signed an agreement to send up a Federal Express satellite in 1989.