The nation's major banks have been complaining for years that they are hamstrung by federal regulations permitting competitors such as brokerage houses to offer banking services while banks are prohibited from offering products such as money market mutual funds that their competitors can offer.

The major banks say their inability to engage in banking operations in more than one state is equally distressing. There is a loophole in the federal laws prohibiting interstate banking -- and both South Dakota and Delaware have taken advantage of it as have major U.S. banks such as Citibank and Chase Manhattan.

While it is true that a customer cannot buy a money market mutual fund from his friendly Riggs banker or find a branch of Contintental Illinois or Citibank on Connecticut Avenue, banks can reach far beyond their home cities or states. If there is some minor-league tinkering with federal bank statutes that now bar interstate branches of U.S. banks, a number of major banks are ready on almost a moment's notice to take advantage of those changes.

Ever since Citibank pioneered the bank holding company -- a corporation created to own a bank -- in the late 1960s, the parent corporations of the major banks have bought companies that federal regulators judge to be closely related to banking or have created their own.

For example, according to an analysis by Manufacturers Hanover Corp., which owns the giant New York bank Manufacturers Hanover Trust Co., 4 of the top 10 U.S. banks holding companies have operations of one sort or another in 30 or more states, not including their home. All of the top 10 banks operate in more than one state.

BankAmerica Corp. and Citicorp control the nation's two biggest banks. BankAmerica has operations in 40 states; Citicorp, in 39. Each has offices in Washington as well. Manufacturers has offices in 30 states and the parent of Security Pacific, the big California bank, is represented in 35 states.

Buying a consumer finance company has been the method the biggest bank holding companies have used to spread around their presence. Manufacturers' finance company has 422 offices in 25 states. Security Pacific has 394 consumer finance offices, BankAmerica 390 and Citicorp 207.

Consumer finance companies make loans to individuals, but cannot accept deposits, the major feature that differentiates them from a bank branch.

But as Manufacturers Hanover Chairman John F. McGillicuddy told a meeting of the corporation's top officers last May, "Many of our consumer finance offices are in excellent locations. We figure that should nationwide branching come -- even next week -- fully a third of these offices could be converted at once into full-service branches."

Of course, as bankers will contend, correctly, having the brick and mortar in place and having a branch are two different things. At the same time, however, major banks are developing a presence and visibility across the country through the holding-company vehicle that will enable many of them to rival the most-far-flung brokerage houses in access to consumer markets.

Not all major banks have operations as widespread as the BankAmericas and the Citicorps of the world. Continental Illinois, for example, which is the third-biggest commercial lender in the country, has 21 offices in 10 states. J.P. Morgan, which controls the blue-chip commercial lender, Morgan Guaranty Trust Co., is in but 4 states.

Neverthless, far-flung operations are not the only indication that banks and bank holding companies range wide in the services they offer. Citicorp Chairman Walter W. Wriston said in a recent interview that Citicorp, through its leasing subsidiary, owns more airplanes than any airline in the world. In 1980 Citicorp's leasing assets were worth $1.8 billion. Manufacturers Hanover's leasing subsidiary had assets worth $2.4 billion.

Many of the big bank holding companies have extensive mortgage-servicing portfolios and run trust and investment advisory offices as well, a domain that brokers would say traditionally has been theirs.

The next time you hear bankers complain that they are being kept out of certain financial markets, believe them. But also believe that many of them not only are operating in a large number of states, but also are providing services and products that few would have envisioned 10 or 15 years ago.

The big banks may be regulated, but they are hardly downtrodden.