Washington area bank companies are racing to merge with one another, hoping to grow big enough and fast enough to survive intense competition from giant New York, California and Chicago banks that eventually may move into the area.

With three major merger agreements recently announced and still more in the works, the metropolitan area's banking landscape is being dramatically recontoured without regard to the once-sacred prohibitions against interstate banking.

The changes in ownership may not have much immediate effect on consumers and businesses in their day-to-day banking. In most of the merger plans announced to date, the parent companies are combining, but the subsidiary banks will keep their separate identities and presumably change very little.

"Did you notice the difference when ITT bought Wonder Bread? Or when it sold it?" asked one key bank official.

But in the long run, according to some analysts, bank customers may benefit from the merger wave as the large regional bank companies jockey for bigger shares of the market and as they prepare to do battle with bigger banks from the major financial centers by wooing customers. The competitive pressure could prompt higher interest rates paid on savings accounts or lower loan fees.

The merger activity has been spurred by new state laws that permit what is called regional interstate banking. Virginia and Maryland have recently approved regional banking bills and the D.C. City Council is considering one.

The laws, which differ only in detail, permit bank mergers and acquisitions in a multistate region, but prohibit participation by bank companies not based in the region. The laws are intended to buy time for local banks to grow stronger before Congress approves nationwide interstate banking.

In just under four months, seven sizable bank companies in the District, Maryland and Virginia have announced merger plans.

Sovran Financial Corp. -- Virginia's biggest bank company, with $8 billion in assets -- recently announced an agreement to acquire D.C. National Bancorp. United Virginia Bankshares Inc., Virginia's second-biggest, has agreed to purchase NS&T Bankshares Inc., the District's fifth-biggest.

Last week Union Trust Bancorp of Baltimore agreed to be taken over by Bank of Virginia Co., and First Maryland Bancorp, the state's second-biggest bank company, announced that it is holding discussions that could lead to a merger with a larger bank company in the region. Informed sources have said First Maryland is talking with United Virginia.

United National Bank of Washington, a smaller D.C. bank with assets of $75 million, announced on Friday that it is talking with several local banks about the possibility of a merger, noting that recent changes dictate "that prudent bankers take the necessary steps to provide and maintain the services their customers and the community both desire and deserve."

The interstate merger fever -- which appears to be highest in this area, New England and the Southeast -- is the tip of what experts said could be a sweeping overhaul of the corporate structure of the nation's banking industry. And unlike most of the mergers of financial institutions in the past several years -- which regulators have orchestrated to clean up after failures -- it is producing combinations of some of the healthiest companies.

Whatever the long-run impact of the changes within the banking industry, one group already has benefited. Shareholders in many bank companies have seen the price of their stock rise markedly in recent months, as legislatures passed regional interstate banking bills.

When Union Trust Bancorp announced last week that it had agreed to be taken over by Bank of Virginia, the price of Union Trust's stock catapulted $16 in one day.

Regional bank-merger activity has been even more pronounced in Florida, Georgia and North Carolina than in the Washington area. But G. J. Manderfield III, president of Bethesda-based Suburban Bancorp, said, "We're going to see an awful lot more before the end of the year."

Neither United Virginia's proposed acquisition of NS&T nor Sovran's bid for D.C. National can be approved -- assuming other regulatory hurdles are met -- until the District approves its version of an interstate banking bill. A bill was approved on its first reading in the council last month, but further consideration has been postponed until September.

Lack of a D.C. law also stymies D.C. banks from moving into Maryland or Virginia.

Virginia and Maryland's interstate banking laws, which took effect July 1, align them with the District and 11 other states in a Southeastern region. So far, the mergers have been concentrated in smaller "natural" markets within the region -- like Maryland, Virginia and the District. But bankers said that eventually bigger combinations will occur within the entire region. Those mergers, which are perhaps several years off, will create giant banks with some $20 billion to $30 billion in assets.

Most regional interstate banking laws are similar.

In Virginia, for example, the law permits a bank holding company from any state in the Southeast to acquire a Virginia bank company as long as the home state of the acquiring firm grants the same privilege to a Virginia bank company. This "your banks can buy my banks as long as my banks can buy your banks" concept is called reciprocity.

Maryland's law has a slightly more restrictive wrinkle. It limits its regional reciprocity to bank companies in Virginia, the District, Delaware and West Virginia until 1987. After that, bank companies in 10 other states would be extended reciprocal privileges.

Some states have included a provision called a "trigger" clause, which would open their borders to national interstate banking after two or more years. The purpose of the trigger is to allow banks in a region to solidify their positions before competition from outside the region is allowed. Although D.C. bankers support a bill without a trigger, Mayor Marion Barry has threatened to veto the measure if it does not include a trigger.

Customers may benefit from the mergers in some ill-defined long run. Not only might big regional banks become more competitive, they might also realize economies of scale in processing paper and gathering funds that could hold down rising bank expenses.

Nonetheless, the swing toward regional interstate banking is designed to help segments of the industry, not customers. This restructuring of an industry along regional lines has evolved primarily as a defense against inroads by big out-of-state banks from financial centers such as New York and Chicago.

Even so, proponents of regional interstate banking maintain that the concept offers several benefits to communities as well as banks. The Coalition for Regional Banking and Economic Development, a group organized to promote regional banking, maintains that strong regional banks know the economy of an area and can better serve their customers.

"Regional banking is a powerful engine of economic development," said Marlin D. Jackson, president of the coalition.

Lawmakers in Maryland, Virginia and the District stressed economic development as a primary reason for backing regional banking legislation.

Massachusetts enacted the nation's first regional interstate banking law in 1982. Neighboring states eventually enacted similar laws, leading to establishment of a so-called New England Compact. In the interim, states in other sections of the country have entered into reciprocal pacts, or agreements to permit limited interstate banking.

The recent flurry of merger announcements was hastened by a Supreme Court decision in June, which gave the green light to regional interstate banking pacts that had been challenged by New York's giant Citicorp and other money-center powers.

The restrictions on interstate banking are firmly grounded in federal law. The McFadden Act prohibits national banks from branching across state lines. At the same time, the Douglas Amendment to the Bank Holding Company Act of 1956 prohibits a bank company from acquiring banks in another state unless the state of the target bank approves.

Laws prohibiting national interstate banking notwithstanding, big banks increasingly have devised ways to get around the ban. Although these banks are prohibited from accepting deposits outside their home states, they have, through devices such as credit cards, consumer finance companies, commercial loan production offices, mortgage lending and so-called limited-service banks, established firm footholds in other states. Technological developments such as automatic teller machines and other electronic banking systems have further extended the reach of larger banks into other states.

Thus, in practice, if not through bricks and mortar, interstate banking is already here, many in the banking industry agree. Indeed, Federal Reserve Chairman Paul A. Volcker, in testimony to a congressional committee this year, suggested that "the days of rather insulated local deposit markets are gone."