Two more Baltimore bank holding companies have received preliminary approval from the Comptroller of the Currency to establish "nonbank" banks in the District.

First Maryland Bancorp, the state's second-largest bank holding company with $4.1 billion in assets at the end of 1984, has received permission to establish First Omni Bank (D.C.) NA. It would offer both retail and commercial loans. Equitable Bancorp, Maryland's third-largest bank corporation with $3.3 billion in assets as of Dec. 31, plans to open a consumer bank, Equitable Bank (D.C.) NA. Equitable is not sure yet what services its nonbank bank will offer, but it will not make commercial loans.

Final approval, however, is required from the Federal Reserve Board, which has been very reluctant to allow any of these institutions.

A nonbank bank either takes demand deposits (checking accounts) or makes commercial loans, but not both. By forgoing one of these functions, a holding company can avoid the federal restriction against interstate banking. The Fed opposes such institutions because their parent companies are acting outside its jurisdiction and because they constitute a bank expansion that has not been sanctioned by Congress.

Four banks besides Equitable and First Maryland have received permission to enter the District, and two more applications are pending. One of the banks that has received approval is based in Maryland; the other three are from as far away as Hong Kong. BankAmerica Corp. of San Francisco and a New Jersey holding company also have applied.

In addition, 19 banks already are based in the District, a situation that has led one D.C. banker to say that the nation's capital is "overbanked" without the nonbank banks.

The Comptroller has approved applications for nine nonbank banks in Maryland; five more are pending. No nonbank banks have been approved for Virginia, but 17 applications are pending. To date, 167 of these limited-purpose banks have obtained prelimary approval nationwide and 208 more applications are pending.

Equitable would like to open an office in Georgetown. Spokeswoman Barbara Lucas said the bank believes a Washington office would be a natural extension of its current business.

First Maryland has received preliminary permission for nonbank banks in Allentown, Pa., and Boca Raton, Fla., as well as the District. It has also applied to open a nonbank bank in Fairfax County.