Reacting to recent sharp rises in its stock, Dart Drug Corp. yesterday denied the existence of any pending sales of subsidiaries or mergers involving the company or its divisions.

Dart's stock, which has risen nearly 20 points since March 15, closed unchanged yesterday at 54 1/4 bid in over-the-counter trading.

In trading Wednesday, the Landover-based company's stock closed at 46 bid, 47 asked, up 1 1/2. It gained 8 1/4 points in trading on Thursday, closing at 54 1/4 bid, 55 3/4 asked.

A company spokesman said he believes the stock rose on Thursday as a result of an article that appeared in The Washington Post. The article quoted analysts who referred to recurring stories about a possible sale or merger of Dart's drug chain with Thrifty Corp. of California.

One analyst also suggested that Dart might spin off the drug chain eventually if it becomes clear that it would be more profitable for the company to focus only on specialty stores such as its Crown Books and Trak Auto subsidiaries.

Dart, however, characterized the speculation as inaccurate.

And in a brief statement yesterday, Dart emphasized that, apart from its proposed initial public offering of stock in Trak Auto, "there are no pending sales of subsidiaries or combinations involving Dart Drug Corp. or any of its subsidiaries."

Dart first announced on Feb. 10 that it was considering a plan to sell part of the discount auto parts and accessories subsidiary in a public offering. The sudden rise in the price of Dart's stock began last week after it had filed a registration statement on the proposed offering of about 29 percent of the stock in Trak Auto.

Nonetheless, Dart Drug Corp.'s strength is in its specialty subsidiaries, and "that's where the company is heading," said Ken Gassman Jr. of Wheat, First Securities.

Gassman noted further that Dart Chairman Herbert Haft's son, Robert, who was elected president and chief operating officer of the corporation last year, "has made his mark" as a specialty retailer.

Robert Haft, who founded Crown Books five years ago and who retains the title of president, built it into a chain of about 100 stores.

Dart Drug Corp. does not report earnings separately for its subsidiaries. But information that it filed with the Securities and Exchange Commission recently shows that Trak Auto Corp.'s operating earnings of $2.19 million for the year ended Jan. 31, 1982, accounted for more than 52 percent of the parent company's earnings.

And although the parent company has not reported results for the fiscal year ended Jan. 31, 1983, the Trak Auto subsidiary had operating earnings of slightly more than $4 million.

"If you look at the results of the Trak Auto operation through Jan. 31, 1982 , it contributed 10.7 percent of revenues and 52.7 percent of profits," Gassman observed. "For the entire year, Trak Auto earned about what the entire corporation earned in the previous year. "And while we don't have any figures for Crown Books, I believe that that is also very profitable," Gassman continued.