Exxon Corp., the world's largest oil company, announced today that it has developed a new way of delivering electricity to industrial motors that could save the nation the equivalent of a million barrels of oil a day by 1990.

Exxon claimed that if its new "alternating current synthesizer" were in full use by 1990, energy consumption by industrial motors could be cut by as much as 50 percent.

This, the company claimed, would be the equivalent in energy savings of one million barrels of oil a day or 100 million tons of coal a year. The United States currently uses about 19 million barrels of oil each day and more than 600 million tons of coal a year.

Exxon said the process was developed by its affiliate, Exxon Enterprises Inc., as an offshoot of research it was doing on electric cars. The technique was invented earlier in the decade by Richard H. Baker, a lecturer at the Massachusetts Institute of Technology.

Baker is a full-time consultant to Exxon now and during the last three years has worked to make his inventions commercially producible.

Exxon President Howard C. Kauffmann said the company has two prototypes in operation - one at its Bayway refinery in Linden, N. J., and the other at its Baytown, Tex., refinery.

The 15 horsepower pump at Baytown has had energy savings of about 35 percent, while the 25 horsepower pump at Linden has recorded savings of more than 50 percent, Kauffmann said. Both prototypes have been in operation since early April.

Exxon said that since it lacks the manufacturing and marketing expertise to sell the process, it is discussing the acquisition of Reliance Electric Co. in Cleveland.

Exxon would give no details of the possible purchase of the $966 million electrical equipment manufacturer. Reliance also declined comment. Kauffmann said Exxon has had some preliminary talks with the Justice Department about the potential acquisition.

Exxon said its new technology permits conventional electric motors that operate pumps, air blowers and gas handling equipment to run at varying speeds, depending upon how much work they have to do. Motors that operate on alternating current - the kind supplied by electric utilities-run at one speed at all times.

Industries now use valves or dampers to increase or reduce the amount of fluid pumped or air circulated. The Exxon technique would make the motor itself go faster or slower by increasing or reducing the amount of electricity that is fed to it.

Exxon said the way most pumps and fans operate now is analogous to having an automobile engine operate at full tilt all the time, controlling car speed by the brakes.

The process is far different from one developed two years ago by California inventor Cravens L. Wanlass with the support of the Southern California Edison Co. The Wanlass invention involves a new design for electric motors that would cut their energy consumption by about 20 percent. The invention is still in the development stage.

The Exxon process leaves the motor untouched, but allows it to run at varying speeds by putting the alternating current synthesizer between the utility and the motor. Exxon officials said there would not have to be any change in the motor itself.

Electric motors account for about 64 percent of all electricity consumption.The process designed by Exxon can be used on motors in the one horsepower to 200 horsepower range (most home motors such as those used in blenders, eggbeaters or food processors are smaller than one horsepower).

These larger motors are used mainly by industries, with 85 percent of them driving pumps or air and gas handling equipment. According to the Department of Energy, roughly 23 percent of total energy consumption is from motors of this variety. Exxon said its process has limited use in consumer products, although home air conditioning systems and heat pumps can make use of the technique.

At a demonstration for reporters today, Exxon used two identical air ventilating machines, one where air flow is controlled by dampers and the other by controlling the speed at which the fan motor operated.

When both were on a full speed, the conventional fan system used 160 watts of electricity while the new system used 170 watts. But when air flow was lowered in the conventional system by partially closing the dampers, consumption rose to 190 watts, because of the back pressure from the air that was not flowing through the partially closed dampers.

When the flow of air was reduced in the new system by slowing the speed of the motor, electrical consumption was reduced to 65 watts.

Exxon officials said there are other techniques that vary the amount of electricity delivered to motors, but they are expensive, bulky and inefficient.

Jo A. Graves, senior vice president of Exxon Enterprises Energy Interest Group, said the company estimates the new process would pay for itself within one to three years, depending upon the application.