The District of Columbia Public Service Commission yesterday ducked the question of whether electric utility customers here ought to help hold down electric bills of Pennsylvania residents who usually get their power from the Three Mile Island nuclear plant.

In an unusual 1-1 vote, with one member absent and not voting, the D.C. agency referred the controversy to the federal Energy Regulatory Commission.

Last fall, Potomac Electric Power Co. asked the PSC for permission to sell electricity to owners of the Three Mile Island reactor for less than Pepco usually charges for power sold to other utilities in the Pennsylvania-New Jersey-Maryland Power Pool, known as PJM.

Since the TMI reactor was shut down by a nuclear accident last year, the plant's owner, General Public Utilities, has had to buy a lot of electricity from other companies.

The commission's approval to cut the price to GPU was needed because the profits Pepco makes on such sales must be shared with its customers.

In effect, Pepco asked its customers to pass up those savings so customers of the TMI plant would not have to pay such high rates for their electricity. Pepco argued that its customers ought not to profit from the troubles of the TMI customers.

Several other power companies asked state utility commissions to give similar discounts to the TMI company. Before any of the requests were decided, however, General Public UTILITIES ASKED FERC to take the case of the hands of the state regulators.

Yesterday, the D.C. commission decided to let FERC handle the whole dispute.

When the final vote was taken, PSC Chairman Elizabeth Patterson was ill and absent, a staff member said. Vice Chairman Ruth Hankins-Nesbitt voted against the plan. Commissioners Wesley R. Long. voted "to take no position," saying the whole case "raises more questions than it answers" and "does not provide a basis for any decision."