Maryland National Bank and American Security Bank will fail to meet federal minimum standards for capital by the end of the year when tougher requirements on this key measure of a bank's financial health become effective, according to a filing with the Securities and Exchange Commission.

The filing is the first public acknowledgment by MNC Financial Inc., the parent of the two banks, that capital levels will fall short of the new guidelines, which are intended to boost the levels of cash that bank owners must provide to protect the federal deposit insurance fund from losses.

While MNC Financial confirmed that capital levels at the two banks are deficient, it declined to disclose the specific levels at either institution. MNC spokesman Daniel G. Finney said the company's attorneys had determined that specific disclosure in the quarterly financial report filed with the SEC was not required.

Lee Cross, spokeswoman for the Office of the Comptroller of the Currency (OCC), which regulates national banks, said that the agency was aware of the capital shortfall and already has taken steps to require the two banks to comply with the law.

American Security Bank and Maryland National Bank must raise capital by March 31, 1991, and must raise the levels again by June 30, 1991. Failure to meet the deadlines could result in further regulatory action, such as closing the institutions or forcing them to merge with healthier banks.

Last month, newly appointed Chairman Alfred Lerner said MNC would sell its prized credit card business to raise the required capital. Banking analysts estimate that a sale of MBNA America, the nation's fourth-largest bank card operation, could provide MNC with as much as $1 billion, plenty of cash to solve the firm's capital woes and position the two banks for future growth.

However, the analysts questioned whether MNC will remain profitable without the credit card operation, which has been the major contributor to MNC's earnings in recent years. Lerner said he believes the future of the bank subsidiaries is strong enough to withstand the loss of MBNA America and he hopes to complete the sale during the first quarter of 1991.

MNC's financial troubles began in the first quarter of this year, when the area's weakening commercial real estate market began to wreak havoc on the bank company's $4 billion portfolio of real estate loans.