Signaling its continued interest in acquiring new companies, Dart Group Corp. yesterday asked the Securities and Exchange Commission for permission to sell $250 million of subordinated debentures due in 1995.

Dart said it would use the money "for general corporate purposes and acquisitions." Dart Chairman Herbert H. Haft and President Robert M. Haft have made it clear that they have been looking for an acquisition ever since the company sold its 73-unit drugstore chain for $160 million.

This year, the company has unsuccessfully sought to buy two major retailers. In early 1985, the Hafts considered a possible takeover of The May Department Stores Co., the parent of The Hecht Co. After May resisted the Hafts' moves by arranging a real-estate deal that would have made an unfriendly takeover difficult, the Hafts sold their stock for a $1.4 million profit. This summer, Dart tried to acquire Jack Eckerd Corp., the nation's second-largest drugstore chain. To ward off Dart, Eckerd agreed to buy back all of Dart's shares, giving Dart a $9 million profit.

Eckerd, based in Clearwater, Fla., meanwhile has said it is considering selling off its chain or merging with another company.

The company, which has about 1,500 drugstores in 15 states, disclosed Wednesday that it has begun preliminary talks with New York investment banker Goldman Sachs & Co. and a few other companies it did not name, but no definitive proposals were made.