JERSEY CITY, N.J. (AP) _ A transformer exploded at an electrical station today, severely burning three workers.

The explosion occurred at a Public Service Electric & Gas Co. substation in a marshy area in this city of 225,000 just west of New York, said police Lt. Richard Kist.

Three utility workers were taken to University Hospital in Newark for treatment of burns. A fourth worker was not burned but was being evaluated at the same hospital for trauma, said Frank Centore, a utility spokesman. Their identities were not released.

Hospital spokesman Rogers Ramsey said one worker is in ''extremely critical'' condition with severe burns and the other burn victims were in critical but stable condition.

Police and PSE&G officials were investigating the cause of the explosion, Kist said. The blast did not cause a fire.

Electrical service to some 50,000 customers was disrupted, but most had their power back on within a couple of hours, Centore said.

The explosion comes less than a week after a natural gas pipeline exploded in Edison, flattening eight apartment buildings and temporarily displacing 1,500 people. Edison is about 25 miles to the southwest.