Maryland's surprise announcement Thursday of an agreement that would permit a Citicorp subsidiary to bank statewide could have a serious impact on steps being taken by neighboring states and the District to form an interstate banking region.

The deal, which would create an estimated 1,000 jobs in a depressed area of Maryland, has drawn strong opposition from Maryland's banking industry.

Concern over the agreement goes beyond the expected impact on intrastate competition, however. Even though it isn't tied to Maryland's interstate banking bill, the Maryland-Citicorp agreement has strong implications for a regional interstate banking movement now under way in mid-Atlantic and Southeastern states.

Under the regional interstate banking concept, which originated in New England, Maryland, 12 other states -- all in the Southeast -- and the District would participate in a regional reciprocal pact. For example, a Virginia bank holding company could buy or merge with a bank holding company in Florida, as long as Virginia accorded the same privilege to Florida banking institutions.

The driving force behind the move toward regional reciprocal banking is growing concern that Citibank and other big money-center banks are poised to swallow up strong regional banks if Congress ever approves national interstate banking. Federal banking law generally prohibits a bank holding company from taking over a bank in another state without that state's approval.

The Citicorp agreement is not part of a regional interstate banking bill currently before the Maryland General Assembly, but is contingent upon approval of a separate bill that would permit Citibank's lone office in Maryland to branch statewide.

In exchange for authority for Citibank Maryland to open branches statewide, Citicorp has agreed to buy Fairchild Industries' abandoned aircraft plant in Hagerstown and convert it into a regional bank-card processing facility.

Keeping giants such as Citibank at bay "was the whole purpose of the regional compacts," grumbled William K. Weaver, executive vice president of the Maryland Bankers Association. If states in the Southeastern region "decide to deal Maryland out" in retaliation for its agreement with Citicorp, Weaver warned, "it would have a devastating effect on us. If Gov. Harry Hughes brings Citicorp in here, we're dead."

Citibank's presence as a statewide competitor might pose problems for Maryland banks but isn't likely to affect competition for District banks, said Michael F. Ryan, president of the D.C. Bankers Association.

Weaver said he was anxious to get the reaction of bank industry leaders in the Southeast. Calls by The Post to several of those officials yesterday were not returned.

Here in Washington, William K. Dabaghi, chief counsel for the Coalition for Regional Interstate Banking and Economic Development, cautioned, "We would be as concerned about Citicorp's long-term goals for the region as the Maryland Bankers Association."

Thus far, five of the 13 states in the Southeastern region, including Virginia, have passed regional reciprocal banking bills. The D.C. City Council is expected to begin hearings on a bill later this month.

Overall, 10 states have enacted regional reciprocal bills, and about 20 others are expected to act this year.

Most reciprocal banking bills are identical, although some states have either proposed or adopted bills that contain "triggers" -- provisions that would automatically sanction national interstate banking after a specified period.

Maryland's bill, for example, contains a trigger that would allow banks from any of the 49 other states and the District to enter the state four years after the law becomes effective. Like most bills, it also contains an anti-leapfrogging provision that bars a bank holding company from buying a Maryland bank holding company if the acquiring company's principal location is outside the defined region. The original Maryland bill would have permitted a holding company from the region to establish a new bank in the state, but several legislators have decided to delete that provision.

The Maryland bill, like Virginia's, would become effective July 1.

Virginia legislators rejected the trigger clause that would have opened the door to national interstate banking after several years. Legislators also wrote in a provision that says a Virginia bank must have been in existence for at least two years before it can be acquired by an outside bank holding company.

The District bill is virtually identical to the Maryland and Virginia bills, though there are no provisions for a trigger to national interstate banking or authority to establish new banks without mergers.