Executives of Security National Bank, the District's eighth largest, said last week that preparations are being made to form a holding company to be known as Security National Corp.

A holding company would enable Security to "take advantage of opportunities that aren't available to a national bank," said Thomas J. Schaefer, president and chief operating officer. A holding company, he said, would be in a position to take advantage of opportunities that might be available if interstate banking is approved.

At least seven of the District's 15 banks, having cited similar considerations, are now subsidiaries of holding companies or have announced plans to form parent organizations.

Officials of Security disclosed the bank's plans as part of a growth strategy that has been developed in conjunction with the recently completed merger with Washington Bank.

The merger, which became effective Jan. 1, is the first involving District banks since Union Trust and First National banks merged in 1976 to form what is now First American Bank of Washington.

As part of the transaction in which Washington Bank was acquired by Security, Leo M. Bernstein, formerly chairman and president of Washington, has been elected chairman of Security. Robert J. Koontz Jr. retains the title of chief executive officer and has been elected chairman of the executive committee.

Security culminated the merger with Washington after an abortive attempt by NS&T Bank to acquire Security last summer.

With assets of $160 million, Security is one of the District's middle-tier banks. However, bank officers characterize it as one of the strongest. Johnston, Lemon & Co.'s 1980 comparison of District banks rates it among the top performers for that year. It has maintained a compound annual increase of 18.2 percent since 1976.

"My conservative bottom-line approach will continue," Koontz remarked.

Nonetheless, the new management team plans "major moves" in recognition of new banking opportunies and anticipated growth in metropolitan Washington, Koontz emphasized in a prepared statement.

The bank plans to expand its automatic teller machine (ATM) network from its nine branch locations to several remote facilities along major arteries used by commuters. Schaefer also said Security is "very much interested" in participating in both ATM regional networks that have been formed by financial institutions in the District, Maryland and Virginia.