E.I. du Pont de Nemours & Co. on Wednesday reported a net loss of $680 million for the third-quarter of 1993 and outlined elements of a major restructuring program.

Meanwhile, Union Carbide Corp. Wednesday reported a 73 percent increase in third-quarter profit, citing a cost-cutting program, equity gains from joint ventures and the elimination of some management positions.Du Pont said that excluding the restructuring and other nonrecurring items from both periods, earnings were 51 cents a share, compared with 56 cents a share for the same period last year. The difference reflects, in part, the effects of the ongoing coal strike on its affiliate, Consol Energy Inc., which lowered Du Pont's earnings by 7 cents a share vs. last year.

Du Pont announced it recorded, in total, an after-tax charge of $1.3 billion, or $1.91 a share, for the restructurings. This includes $375 million, or $.55 a share, related to personnel separation costs resulting from job reductions, which were announced previously. At that time the company also indicated it anticipated other restructuring charges for the third quarter. These amounted to $920 million, or $1.36 a share.

The restructuring charges are directly related to corporate decisions to reduce worldwide employment levels and aggressively realign production and support facilities to further improve productivity. These actions are expected to substantially reduce fixed costs in the future.

Union Carbide reported profit of $38 million, or 23 cents a share, in the quarter, up from $22 million, or 14 cents a share, during the same period last year.

Sales were down in the quarter to $1.13 billion, from $1.24 billion during the same period last year, as prices for some chemicals "remain at historic low levels," said Robert D. Kennedy, Union Carbide chairman.

The third-quarter results included an after-tax gain of $30 million from the sale of the company's organosilicon business in July. But that gain was offset by a $30 million restructuring charge for a plant closing in Canada.

For the first nine months, Union Carbide reported a profit of $24 million, or 10 cents a share, on sales of $3.6 billion, compared with a loss of $194 million, or $1.57 a share, on sales of $3.7 billion during the same period last year.

The nine-month results included an after-tax charge of $97 million in 1993 and $361 million in 1992 for accounting changes to reflect the company's liability for future benefits paid to retirees and income taxes.