Riggs National Corp., parent of the District's largest bank, announced yesterday that it will extend its reach into the Maryland suburbs with the acquisition of a small, fast-growing Rockville bank.

Riggs has agreed to acquire all of the stock of First Fidelity Bank in exchange for Riggs stock worth roughly $19 million at current levels.

With the acquisition, subject to the approval of regulatory authorities, Riggs will have completed the expansion of full-banking services to all three Washington area jurisdictions. Last year, Riggs crossed the District line for the first time with the purchase of Guaranty Bank and Trust Co. of Fairfax.

Bank executives have said a regional presence is critical for banks to cope with the increased competition in the industry. And in recent years, several Maryland and Virginia institutions have purchased banks across state lines.

A Riggs spokesman said the First Fidelity deal is expected to be completed within six months. First Fidelity is expected to be merged into a new subsidiary of Riggs called The Riggs National Bank of Maryland. Riggs officials calculated that they would be paying roughly 2.6 times the book value of First Fidelity, a price in line with recent bank mergers in the region.

With First Fidelity, Riggs is acquiring a small, but fast growing, bank that has catered mostly to small businesses and professionals. As of March 31, First Fidelity reported total assets of $67.1 million and deposits of $56.5 million. First Fidelity Chairman Jay FitzGerald said the bank reported after-tax profits of $387,000 in 1986 ($1.30 a share). He said deposits grew 91 percent in 1986.

First Fidelity's main office is in Rockville with a branch in Clinton. The bank plans to open two additional offices at undisclosed locations by the end of the year.

First Fidelity was founded in 1984 with an initial investment of $3.7 million -- half from 20 investors led by FitzGerald and half from outside investors.

While Riggs already has many individual and corporate customers in Maryland, the move to establish full operations there is seen as an acknowledgement that suburbanites no longer necessarily come to the city to work and do business. With the new acquisition, analysts said, Riggs will have increased access to thousands of potential upscale clients in the Maryland suburbs.

Riggs Chairman Joe Albritton said in a statement that the deal "will enable Riggs to complete establishment of a strong presence in all of our key market areas."

"This allows them to tap a market more effectively than they have to date with a service area that is confined by the Washington borders," said Gilbert W. Keech Jr., who follows regional banks for Washington brokerage Johnston, Lemon & Co.

Keech also said the purchase makes Riggs itself a more attractive acquisition candidate, although Albritton repeatedly has stated his intention to keep Riggs an independent company. As of March 31, Riggs National Corp. had assets of $5.92 billion.

Under the agreement, First Fidelity's current management will remain with Riggs, and its existing board will continue to serve the Riggs National Bank of Maryland. "They said they are not going to interfere in any way," said FitzGerald. "If we don't produce, then we're history."