Executives of Maryland National Bank, which today opened its first out-of-state office in the District of Columbia, are studying Pennsylvania, Virginia and West Virginia as possible banking market places by the mid-1980s.

Maryland National Corp. Chairman Robert D. H. Harvey said today he expects Congress and much of the banking industry to approve interstate branching in contiguous states "within the next two or three years."

And Maryland National, already the largest banking firm in the Maryland-D.C.-Virginia region, is planning to maintain that status by being ready to take advantage of changes in federal laws that now prohibit full-service branch banking across state lines.

"We think the initial thrust of legislation is in fact going to be regional, and we are gearing our plans on that basis," Harvey said in an interview.

The office opened in downtown Washington today by Maryland National is limited in the business that can be conducted there, because of existing laws.

Located at 1110 Vermont Ave. NW, the Maryland National facility is called a loan production office, and it cannot take retail deposits or offer checking accounts.

However, the D.C. office will offer a broad range of banking and international financial services to business and government customers in competition with Washington-based banks.

Harvey emphasized, in particular, cash management services for such groups as trade associations that have annual revenues of more than $2.5 million. This is a growing business sector in Washington and many of the city's banks already offer similar cash-management plans for various-sized groups.

Although Maryland National's decision to go into business in the District is a significant step in recognition of a growing Baltimore and Washington business combination, it is not the first bank to enter the rival marketplace. Earlier this year, First National Bank of Maryland opened a loan office at 1800 K St. NW, and American Security Bank of Washington opened a similar office here.

But Maryland National's office in D.C., headed by manager Gracia Martore, has an unusually large initial staff of about a dozen persons instead of the typical two or three professionals in many such out-of-state offices.

Harvey said today the loan office in the District would be the focus for aggressive selling of loans to business customers in the Washington area. At the same time, he said the large office in the District would allow thorough study and experience in that market so Maryland National is prepared when interstate banking becomes a reality.

Maryland National, with assets of $4 billion on Sept. 30, also is taking advantage of liberalized banking laws in Delaware with plans to set up a new bank there, as a center for credit card operations.

Applications for the new bank already have been filed with federal regulators and Harvey said he expects the new Delaware institution to open by late this year. After Maryland National's MasterCard business is transferred to the Delaware subsidiary, cardholders will be assessed an annual service fee--a charge specifically prohibited by Maryland law and a major factor in the bank's decision to move this business out of state.

A number of other banks in Maryland, Pennsylvania and New York are planning separate banks in Delaware for a variety of purposes, including separate credit-card operations. Maryland also has interest-rate ceilings for credit cards. The combination of Maryland laws has caused banks in the state with large credit-card operations to lose money for the past two years on this business.