Today is D-Day for Dart Drug Stores Inc. -- the day the company's debt restructuring package is due to expire at 5 p.m..

If the company fails to receive 85 percent of its year-old bonds -- in exchange for a package of Dart stock and lower-yielding bonds -- Dart has said it may have to file for protection from its creditors under the bankruptcy laws.

Yesterday, Dart issued a statement saying that only 10.7 percent of the bonds had been turned in as of 11:30 a.m. Thursday.

Although Wall Street investors yesterday appeared somewhat surprised at the low response, they cautioned it did not necessarily mean that the deal was in trouble.

Sources close to Dart yesterday said the company remained confident it could achieve its goal of getting 85 percent of the outstanding $160 million bonds exchanged for the new securities package.However, some investors said it could be a close call.

"I think it may be a tight deal, real close," said one investor who declined to be identified.

Burdened by a massive debt, Dart proposed a debt-exchange offer last April in an effort to cut its annual $28 million interest payments.

After several discussions with major bondholders, Dart improved its initial offer; currently Dart is asking bond holders to exchange each $1,000 12.7 percent bond for a package of new securities worth about $766. The package consists of a $500 bond that will bear an initial 6 percent rate and increase by 1.1 percent at every semi-annual interest payment as of 1990. Additionally, bondholders would get 24 shares of common stock, estimated to be worth about $3.50 a share, and 40 shares of preferred stock, each convertible into 1.3 shares of common stock.

"If the exchange offer is not successfully consummated, the company may be forced to seek a reorganization under Chapter 11" of the bankruptcy laws, Dart has said in filings at the Securities and Exchange Commission.

"Under certain circumstances, the company may be forced into liquidation under Chapter 7 of the bankruptcy code," Dart added.

If successful, the debt-exchange proposal is expected to cut in half the company's annual interest payments.

As a result, Dart would immediately become profitable. With the company's huge debt load, its liabilities exceeded its assets by more than $32 million last year.

Dart has already failed to make a $10.2 million interest payment on the $160 million bonds. The payment was due June 1. But Dart said the bank in charge of paying the bond interest had not officially declared the company in default on July 1, in anticipation of the successful debt-exchange proposal.