The D.C. Public Service Commission approved an experimental program yesterday that will enable Potomac Electric Power Co. to limit electrical service next winter to some residential customers with delinquent bills.

The commission also gave Washington Gas Light Co. the right to charge discount gas rates to former customers who can burn No. 6 fuel oil for heating.

They are among the heavy-use customers known as the "interruptibles" because they are subject to service interruptions during cold weather when WGL can't supply the needs of all its customers.

This discount program will remain in effect through October and can be offered only to former customers who use No. 6 grade fuel oil. It is designed to enable WGL to woo back customers who switched to heating oil because of cheaper prices and allows WGL to participate in a program already approved by the Federal Energy Regulatory Commission.

Yesterday's action is in addition to a permanent discount rate structure for interruptibiles that was approved by the commission in March. The permanent discount rate applies to a wider group of customers who use Nos. 2 and 4 grade oils as well as No. 6. The permanent discount rate changes monthly in response to market conditions.

Both actions have been opposed strongly by heating oil companies, because they come at a time when heating oil prices have declined and natural gas prices have risen, making heating oil more competitive.

Commission officials said that the discount will result in a small decrease in residential gas bills because 80 percent of the profits from the discount program will be applied to the cost of supplying residential gas.

Under Pepco's service limiter program--so called because of the device installed in the affected households--delinquent customers who have been given a date for termination of electrical service will receive 10 additional days to make arrangements with Pepco to pay their bills. During those 10 days, Pepco will reduce the amount of electricity supplied to the customers, giving them only enough electricity to meet essential needs such as food refrigeration, lighting and electric starters for gas or oil-fired heat.

Households that are electrically heated or occupied by the elderly or disabled are exempted from the service limiter program.

Pepco sought the service limitation to increase its ability to collect unpaid bills during the winter.

When temperatures are 32 degrees or below, there is a city-imposed moratorium on completely cutting off electrical service to protect delinquent residential customers from the cold. However, the service limitation will be permitted during the winter months when the moratorium on shut-offs is in effect.

A Pepco spokesman said that a similar program was in effect in Maryland this past winter, and more than 75 percent of the people who had their service limited worked out satisfactory payment arrangements with Pepco without having to lose electrical service.