Dart Drug Stores Inc. yesterday significantly sweetened its debt exchange plan in an effort to lure bondholders and creditors to exchange debt for Dart stock as a way to reduce massive interest payments and avoid filing for bankruptcy.

In a document filed late yesterday at the Securities and Exchange Commission, the 81-store chain upped its initial offer, made in late April, in which Dart was asking that each of its $1,000 bonds be exchanged for about $730 in new securities.

In its latest proposal, Dart is seeking to exchange the bonds for more than $762 in new, higher-interest securities. In addition, the new securities would appear to be structured in such a way to persuade a greater number of bondholders to accept the exchange because it would give them a greater equity stake in Dart.

Dart is seeking a similar swap with its major creditor, the Equitable Life Insurance Society of the United States, which holds a 13 percent, $25 million note.

Dart, faced with more than $28 million in yearly interest payments and with liabilities that exceed assets by more than $32 million, has said it needs to reduce its massive junk bond debt or else file for bankruptcy.

"If the exchange offer is not successfully consummated, the company may be forced to seek a reorganization under Chapter 11 of the bankruptcy code," Dart reiterated in yesterday's filing. "Under certain circumstances, the company may be forced into liquidation under Chapter 7 of the bankrupcy code."

In Dart's initial offering, the company had proposed exchanging each of Dart's $1,000 bonds -- with a 12.7 percent interest -- for a new 6.5 percent bond worth $500 and 35 shares of Dart common stock, each valued around $6.70.

Wall Street sources had indicated that most bondholders were confident that a swap could be reached to avoid bankruptcy. However, they noted yesterday, many bondholders were seeking better terms for the high risk securities they bought last summer. Today, these bonds, which had a face value of $1,000 when issued, sell for $400 or $500 each.

To meet the concerns of bondholders with whom Dart has been meeting the past few weeks, Dart now proposes to raise the interest rate on the new bonds and issue new convertible preferred stock.

Under its proposal, each $1,000 bond would be exchanged for a $500, 8 percent interest bond due in 1992 -- a year earlier than the initial offering, and what would amount to 75 shares of common stock. These shares would include 25 common stock shares and five shares of a new convertible preferred stock, each worth 10 shares of common stock. Additionally, Dart would give each $1,000 bondholder 25 shares of common stock valued at about $3.50 each, after the dilutive effects of the convertible stock.

The SEC filing also indicates that management would have to meet tighter requirements before it could receive stock options. Previously, it could have received options on $2.1 million shares. Under the new plan, management would be able to receive options on only $1.4 million shares, but only if the company earns $30 million, before interest and taxes, for the two years ending July 31, 1989. For the fiscal year that ended July 31, 1986, the company earned $12.3 million before taxes and interest. Dart said sales improved 6.4 percent for the first five months of this year.