Dart Group Corp., stepping up its efforts to take over Stop & Shop Cos. Inc., said yesterday it had won enough support from Stop & Shop stockholders to call a special shareholders meeting to consider ousting the Boston-based retailer's board.

The call for a shareholders meeting -- tentatively scheduled for March 30 -- represents a new tack in Dart's efforts to take over Stop & Shop. Dart -- which is controlled by Washington's Haft family -- also is offering to buy Stop & Shop for $1 billion. So far, Stop & Shop has rebuffed the Hafts' overtures, and has said it is talking to other possible buyers.

But Dart said yesterday it had sent a letter to Stop & Shop's board warning the company that it may sue if Stop & Shop accepts an offer from another suitor designed specifically to block Dart's takeover bid. Dart also repeated a request to meet with Stop & Shop management to discuss the offer, something Stop & Shop so far has refused to do.

"All terms of our offer, including price, would be negotiable," Dart Chairman Herbert Haft wrote Stop & Shop in the letter, sent earlier this week and included in a Dart filing with the Securities and Exchange Commission yesterday.

Dart said yesterday that under the provisions of Massachusetts antitakeover law, it had won commitments of support from more than the necessary 10 percent of Stop & Shop stockholders to call a special stockholders meeting. Dart, which owns 2.7 percent of Stop & Shop stock, wants the meeting for a vote on a new slate of directors that would be favorable to Dart's plans to take over the company.

Dart asked that the meeting be held on March 30, but under Massachusetts law, Stop & Shop may be able to set a different date.

Stop & Shop officials had no comment on Dart's announcement yesterday. It came as the firm -- which owns the nation's ninth largest supermarket chain and Bradlees department stores -- was reviewing takeover offers from several other parties.

Although Stop & Shop declined to name those suitors, sources close to the company said yesterday that there were three possible buyers -- all investment banking firms that are attempting to arrange a leveraged buyout of the company in which the management of Stop & Shop would be able to continue to remain in charge.

Speculation about possible buyers centered on Boston financier Thomas H. Lee, Los Angeles merchant banking group of Riordan, Freeman & Spogli and New York investment banker Kohlberg Kravis Roberts & Co. -- all of which have been active in financing leveraged buyouts.

However, Haft said in his letter to Stop & Shop that if the company enters into any agreement "designed to make more costly our acquisition of Stop & Shop" -- such as granting options, special lockup rights, fees or inducements to the purchaser -- then Dart will litigate.

Dart formally launched its takeover bid for Stop & Shop earlier this month, offering $31 a share and subsequently increasing the bid to $37 a share.