The United States and Japan have signed an agreement calling for cooperation in the preliminary design of part of America's planned $8-billion space station, NASA announced. Under the agreement, Japan will develop a laboratory module and an exposed work deck that would be attached to the modular space station to be assembled in orbit in 1993. The memorandum of understanding covers two years of design work. Japan is expected to spend $22 million in the design phase. The National Aeronautics and Space Administration signed a similar agreement with Canada on April 16.