Dart Group Corp., which Wednesday offered about $840 million for Boston-based Stop & Shop Cos. Inc., will have to wait for an answer on its offer.

The board of Stop & Shop, which owns 114 Stop & Shop Supermarkets and 171 Bradlees Department Stores, said yesterday that it would "review the proposal and respond in due course." Company officials declined to comment further on the offer by Dart Group, which is owned by Washington's Haft family.

However, one source close to Stop & Shop said he would be surprised if the company viewed the Hafts' offer favorably.

If it decides to repel Dart's offer, Stop & Shop could try to scare the Hafts away by triggering a "poison pill" takeover defense that the 80-year-old company put into place in 1986. A "poison pill" is designed to make any takeover attempt that is not approved by directors of a company prohibitively expensive.

The Hafts on Wednesday offered $30 a share for Stop & Shop's 27.9 million outstanding shares. Stop & Shop stock closed at $29.25, up $3.12 1/2, one of the largest net changes of any stock yesterday. More than 1.2 million shares were traded.

Robert Haft, president of Dart Group, said yesterday that he hoped the Stop & Shop board would not resist the offer. "We would hope that the board wouldn't stand between their shareholders and this $30 offer," he said, noting that Stop & Shop stock traded for about half that amount a few weeks ago.

The Hafts, who control the Crown Books Corp. and Trak Auto Corp. chains and formerly owned Dart Drug, have unsuccessfully tried to acquire several other retail chains in recent years. They have said they are prepared to commit a substantial amount of capital to the bid for Stop & Shop, although they have not specified an amount. Paine Webber Inc., the Hafts' financial adviser in the takeover attempt, has said it is confident it can arrange the remaining financing for the deal.

Harry E. Wells, a securities analyst with Adams, Harkness & Hill of Boston, said he was not convinced that the Hafts are serious about acquiring Stop & Shop. "If you really want to operate stores and not make money in the stock market, why not buy a chain that's for sale?" Wells said. "I think they {the Hafts} think this is an operation with a long, proud family tradition who will want to pick their own owner or own it themselves. ... Why bid up a premium for a store that doesn't want to sell?"

But Robert Haft said, "We made a full and substantial offer, and we have a desire to acquire the business with the management and the employees. We have both the desire and the capability." He said Dart Group officials hoped to meet soon with Stop & Shop executives.