Huntsman Chemical Corp. and GE Plastics have dedicated a $60 million plant in Selkirk, N.Y., which will produce 100 million pounds of plastics used in products such as automobile instrument panels and computer housings, a spokesman said.

"These dedication ceremonies mark the culmination of an exciting and fruitful joint venture agreement between GE and our company," said Jon M. Huntsman, chairman and chief executive.GE, a holding of General Electric and a company which Huntsman Chemical has supplied with polystyrene, will operate the plant producing polystyrene and modified polyphenylene oxide.

Glen Hiner, senior vice president of GE Plastics, called the joint venture a "unique marriage of customer and supplier, one that gives both companies the ability to extend product lines, enhance quality and increase sales volume."

Huntsman Chemical, headquartered in Salt Lake, is the country's largest privately held chemical company and largest polystyrene producer in North America, a spokesman said. Revenues for its polypropolene and compounded specialty manufacturing facilities in 1988 are expected to exceed $1 billion.

GE Plastics' sales of plastic products in 1988 are expected to reach $3 billion.