A suit was filed today on behalf of depositors who claim they lost more than $11 million in the now defunct American Bank & Trust Co., naming the Federal Deposit Insurance Corp. as a defendant along with 22 individuals associated with the bank that collapsed in September, 1976.

Most of the plaintiffs in the suit are citizens of Mexico and other foreign countries who maintained accounts with the bank which, because of what they claim was a massive fraud, were never documented as liabilities on the banks books. Instead they were deposited in a Belgian bank that became insolvent, a Panamanian shell corporation and in commercial paper for the holding company for American Bank & Trust Co., which also became insolvent.

When ABT was colsed Sept. 15, 1976, the FDIC as receiver assumed the assets and liabilities of the bank, eventually selling them to Bank Leumi Trust Co. of New York while making good on any deposit losses.

The FDIC however has ruled that the $11 million at issue in the suit have not been verified as legitimate deposits and are therefore not subject to restitution.

The suit charges the FDIC ruling "constitutes inequitable and unjust discrimination" and that the federal banking agency is involved in "a flagrant conflict of interest" because it has given itself a preferential lien against ABT's assets while rejecting the plaintiffs claims as depositors.

It also raises questions about the role played by John G. Heimann, currently U.S. Comptroller of the Currency and formerly superintendent of banks for the state of New York.

The suit, filed in the New York Supreme Court (a lower court), notes that a cease and desist order was issued against ABT in Septmber, 1975, by the New York Superintendent of Banks to discontinue certain "unauthorized and unsafe," practices. It also notes that the state superintendent's office was examining the bank's books beginning March 5, 1976, and should have uncovered the irregularities that led to the banks eventual collapse on Sept. 15.

Heimann was New York Superintendent from the date when the cease and desist order was issued by his office through the period of ABT's insolvency. As comptroller, Heimann meanwhile is one member of the three-person FDIC, which regulates banks and also insures depositors.

According to the suit, Heimann took part in the FDIC decision to disallow the $11 million in depositors' claims while he "has personal familiarity with the circumstances of the fraud which was responsible for plaintiffs losses and with the reasons for ABTs liability to plaintiffs."

It adds that as superintendent he "failed to take timely action to stop these fraudulent activities. A number of plaintiffs deposited money in ABT for the first time after March 5, 1976."

The FDIC and Heimann had no immediate comment on the suit, which is one of several that have been filed against it in connection with the ABT insolvency.

The case is unsual because it involves the disputed losses to depositors. In the well publicized failures of such billion dollar banks as U.S. national of San Diego only shareholders have wound up losing money while the FDIC has always made depositors whole.