The two firms plan to join forces in building factories that use computers to control assembly lines. San Francisco-based Bechtel Group will design and construct the buildings while Hewlett-Packard, which is based in Palo Alto, will install the computers, according to an announcement by the two firms. The companies have not yet signed contracts but plan to market themselves as a team when they bid for projects, a Bechtel spokesman said. Under the agreement, whenever Bechtel wins a contract to build a computer-driven factory, it will offer a subcontract to Hewlett-Packard for the high-tech gear. Similarly, when Hewlett-Packard wins a contract for a computerized assembly system, it will ask Bechtel to construct the building.