When Exxon Corp., the world's largest oil company, bought Reliance Electric Corp. in 1979, Exxon said it needed the expertise of one of the nation's largest electrical-equipment manufacturers to make and market a new kind of motor that would save the nation the equivalent of a million barrels of oil a day by 1990.

But today Exxon announced that the invention it trumpeted so highly in 1979 is a bust. Its so-called alternating-current-synthesis technology, which worked in prototype, cannot be produced cheaply and reliably enough to compete "with alternate products under forseeable conditions," the company said in a statement.

When it announced its discovery and its intention to acquire Reliance, Exxon said it had developed a process that would permit electric motors to run faster or slower, depending upon the need. When a motor runs slower, it uses less electricity. The invention would have the widest application for motors driving fans or pumps.

Most motors that run on alternating current -- the kind supplied by the local utility -- run at full speed all the time. Dampers or valves are used to reduce the flow of air or fluid.

Exxon not only bought Reliance. It bought a passel of opposition. The $1.2 billion acquisition was challenged as an antitrust violation on many fronts.

But Exxon doggedly pursued the merger and bought Reliance.