When the Potomac Electric Power Co. automatically switched Arnold J. Roccati's air conditioning off and on the past three summers during the utility's periods of peak demand, he didn't feel a thing.

Roccati, a physicist who lives in Potomac, said he never even knew when the air conditioning was on or off. "I was surprised at the number of times Pepco had utilized the feature because we had experienced no discomfort and were not able to tell when the equipment was operating," Roccati said.

Results of Pepco's three-year experimental residential program to cut peak demand for power indicate Pepco could defer the construction of a costly new generating plant if such a program were applied on a larger scale, said Michael Maher, Pepco's manager for energy management development.

"We have about 220,000 residential customers with central air conditioning. So, if a program were instituted that reached a significant percentage of these people, then we would have reduction of a substantial size in megawatts. . . . That's a large chunk towards replacing a very capital-intensive generating unit," he said.

A new 480-megawatt plant would cost PEPCO about $635 million in 1983 dollars, said Carol Lippincott, a Pepco spokeswoman. On the other hand, wider application of residential programs to control peak demand could save Pepco $4 million a year.

In the three-year experiment, which ended in 1983, 700 Maryland and District residents volunteered to have their air conditioners switched off remotely by radio signals -- but on no more than 15 days out of the summer season, said Lippincott. Air conditioners were switched off every 13 minutes in each half hour between 3 and 7 p.m. during the summer season, she said.

Results indicate wide customer acceptance of the program, Pepco's Maher said. "In a survey sent to participants, Maher said 80 percent responded that the program was satisfactory or very satisfactory, and only 1 percent called it unsatisfactory.

Pepco is considering approaching the Public Service Commission to combine the residential program with programs for business and government customers.