Potomac Electric Power Co.'s outlays for new plant and equipment this year will total about $145 million, chairman W. Reid Thompson said yesterday. The Pepco chief also said a rate increase for Maryland customers will be proposed in the near future.

In 1976, the Washington-based electric utility spend $122 million for new property and plant construction, the lowest capital spending since the early 1970s because of cutbacks in electric consumption growth here.

Addressing securities analysts in New York yesterday. Thompson also said Pepco would spend $170 million in 1978, $125 million in 1979, $145 million in 1980 and $190 million in 1981 - a grand total of $775 million over the five years to expand facilities in anticipation of continued, but modest, growth.

During next year, Pepco anticipates raising at least 70 per cent of the needed outlays from internal operations with "no more than" 30 per cent to be financed through the sale of securities or other outside financing, Thompson said.

By the end of the year, Pepco also plans to retire all short-term borrowings and should have some short-term investments as 1978 begins, he added.

Thompson did not specify the amount of rate increases to be sought from the Maryland Public Service Commission later this year. A $45.5 million rate increase has been proposed by Pepco in the District and a $3.2 million boost is being sought for a small area of Norther Virginia served by the firm.

Although Pepco suffered a slight decline in profits during the second quarter of 1977, earnings advanced during the summer months with heavy use of air conditioners. Nine-month profits totaled $65.7 million ($1.42 a share) compared with $56.4 million ($12.5) in the same period of 1976.