The value of Dart Drug stock has surged and then slipped in the last two days in response to an announcement of plans to sell to the public 1.8 million share of common stock in Trak Auto Corp., Dart's auto supply subsidiary.

At the close of business Tuesday, Dart's stock was selling for $35 1/2 per share. On Wednesday, the stock closed at $48 1/2, a 13-point gain. Yesterday, the Dart stock dropped back to $46 per share.

The run-up in Dart stock started after Trak Auto on Tuesday issued a prospectus for its initial public stock offering. Dart, which now owns all of Trak Auto, plans to sell about 29 percent of Trak to the public but will retain a 71 percent stake in the company.

The registration statement filed with the Securities and Exchange Commission gives the transaction a proposed value of $29 million, based on a price of $16 a share for Trak. At that price, Dart's 71 percent share of the company would have an effective value of $71 million.

One analyst suggested the rise in the Dart stock reflects investors' recognition of the "hidden value" of Trak to the parent company.