Dart Drug Stores Inc. said yesterday the 81-store chain had won a new lease on life by completing a financial restructuring plan.

Even though Dart narrowly missed its target of getting the holders of 85 percent of its $160 million in outstanding high-interest bonds to swap them for a combination of lower-rate notes and stock -- and extended its self-imposed 5 p.m. Friday deadline seven hours until midnight -- chairman Stephen H. Hansbrough said early yesterday that 82.5 percent of the bonds had been swapped.

Hansbrough said the chain had won "the window it needs to grow and put its plan into place. We now have the money to put in changes we have promised our customers," including remodeled stores and computerized checkouts, he said only minutes after the deal was completed.

The completion of the restructuring should also solve a stocking problem in the stores, Hansbrough added. Because Dart's suppliers were concerned about Dart's financial health, they had been reluctant to send a lot of merchandise to the stores, Hansbrough said.

"We have experienced a shortage of merchandise in the stores. Now we should get in stock again," he said, adding he planned to notify vendors first thing Monday about the successful financial restructuring.

Faced with massive debt and large annual interest payments, Dart had asked holders of its $160 million high-interest bonds to swap them for Dart stock and new, lower yielding bonds.

Dart had said it needed 85 percent of the bonds to be exchanged if the restructuring was to be successful. Otherwise, the company said it might have to seek protection from its creditors under federal bankruptcy laws.

Dart had set a deadline of 5 p.m. Friday to complete its offer. But then, announcing it had received only 50 percent of the bonds, Dart extended the deadline until midnight Friday.

In total, only 82.5 percent of the debt was swapped. Although that was somewhat less than Dart had hoped for, Wilbur Ross, managing director of Dart's investment firm, Rothschild Inc., said it was adequate to meet Dart's financial needs. Ross said Dart could have lived with an 80 percent return rate.

Yesterday, Dart officials denied there was a last-minute snag in the deal and attributed the delay to the mechanics and paperwork needed to complete the deal -- not to gain time to win more bondholder support.

Dart proposed its debt-exchange offer in April in an effort to cut its annual $28 million interest payments and wipe out Dart's deficit. With the company's huge debt load, its liabilities exceeded its assets by more than $32 million at the end of its last fiscal year.

The debt-exchange proposal called for bondholders to exchange each $1,000, 12.7 percent bond for a new package of securities worth about $766. The package consists of a $500 bond that will bear an initial 6 percent rate and increase 1.1 percent at every semiannual 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.

Also being asked to exchange debt for the new package of securities was Dart's biggest creditor, Equitable Life Insurance Co. of the United States, which held a $25 million note. Equitable agreed to the swap.

Under the 82.5 percent acceptance of the restructuring proposal, Ross estimated the company's yearly interest payments would drop to $13 million and the face value of debt would decrease by $76.3 million. The company's deficit would turn into a net worth of about $4.8 million.

About 40 percent of Dart's stock will now be publicly traded over the counter. Trading will begin 10 days from Monday