The management of Equitable Bancorporation, fighting a takeover attempt by an investor group, has charged that former bank executives who stand to gain by the takeover has used privileged information illegally in connection with the sales of their own Equitable stock.

Court papers filed Thursday also reveal that Samuel Zell, one of the three investors seeking 40 percent of the bank's stock, was indicted in 1976 in connection with a federal investigation of Bahamian tax shelters. The charges against Zell were dropped in 1977 in exchange for his testimony.

The case ultimately resulted in a two-year prison sentence for Zell's brohter-in-law, Roger Baskes, who was convicted of conspiracy to evade taxes on $700,000 earned in connection with the sale of a Reno, Nev., apartment complex.

Equitable, Maryland's third-largest bank, with assets of more than $2 billion, filed its suit in federal court in Baltimore late Thursday, hours after bank Chairman Owen Daly II announced at the company's annual stockholders meeting that the bank's board had voted unanimously to oppose the stock purchase offer by LZH Associates.

Andre Brewster, a Baltimore lawyer representing LZH, said he has reviewed the complaint and "finds it to be totally without merit. We're going to continue to doing the same things we would have been doing anyway."

In a letter to stockholders, Daly noted that the bank's financial adviser, Kidder, Peabody & Co., had concluded that the offer is inadequate and urged stockholders to reject the tender offer.

Equitable has hired Skadden, Arps, Slate, Meagher & Flom, a leading New York tender offer law firm, to handle the case along with George Ball of Lower & Stockbridge of Baltimore. The bank's counsel in most matters, Venable, Beatjer & Howard, is representing two former bank officers involved in the stock sale.

Ironically, the bank also has hired Hill and Knowlton Inc., the Washington public relations firm that represented Joe L. Albritton in his successful bid to acquire controlling interest of Washington's Riggs National Bank.

The investors, Zell, Alfred Lerner and F. Philip Handy, already have an agreement to purchase 1,071 million shares of Equitable stock from nine stockholders at $27.50 a share. They also have made an offer for an additional 510,000 shares at the same price.

The decision, which followed an eight-hour meeting of the bank's board the previous night, sets up a confrontation between -- on one side -- Daly and the bank's management and -- on the other side -- John A. Leutkemeyer, 70, a well-known Baltimore figure who is a former Maryland state treasurer and former chairman of Equitable, and Robert G. Merrick, former chairman of Equitable Trust Co., the predecessor company of Equitable Bancorporation.

Luetkemeyer and his wife have agreed to sell 95,000 shares of their stock to the three investors. Merrick, now a partner with the investment firm of Alex. Brown & Sons, which will receive $350,000 as a commission in the sale, has agreed to sell 112,036 shares.

Equitable charged in its court suit that Luetkemeyer and Merrick, who were directors of the bank until they were not renominated for election at the shareholders meeting Thursday, "were in a position to know, or had access to, material nonpublic information" about the company's bank subsidiary. a

Charging that the agreement and the tender offer, which is contingent on consumation of the initial sale, "violate a plethora of federal and state securities and bank regulatory laws." Equitable asked the court to block permanently the investors from acquiring the stock.

Equitable also charged that the investors did not seek approval of the Federal Reserve System or the Maryland Bank Commissioner, necessary since the purchase effectively would shift control of the bank to LZH. The bank also charged that LZH failed to disclose important financial information, the source of funds for the tender offer, and that Lerner is a director of a large Ohio bank.