Marble banks, stainless steel vaults and brass teller cages give Washington financial institutions an air of permanence that belies the uncertainty of their future.

Ask a handful of bank presidents what their business will be like in five, 10 or 20 years and the replies forecast a revolution in the way people manage their money:

* The elegant names chiseled in stone on graceful buildings will be all that remains of some of the city's oldest banks, long since transformed into local branches of financial conglomerates or merged into regional mega-banks.

* The biggest bank in town will no longer be Riggs, Maryland National Bank or United Virginia Banks, today's local financial giants. More likely it will be Citibank, Continental Illinois, BankAmerica or Sears.

* The imposing bank structures will be replaced or recycled into store-front service centers and money machine boutiques.

* "Going to the bank" will mean visiting an automatic teller machine or typing a transaction into a home computer. The friendly smile of a human teller will be too costly to waste on routine deposits and withdrawals.

* Savings and loans associations will mostly follow trolley cars into history. The S&L's that survive will be like the preserved facades of the 19th century buildings at Georgetown Park -- fronts for modern financial centers.

* Borrowing, lending, saving and investing all will be done at the same place by many people who now use a bank, a stock broker, a savings association, a life insurance company and a credit card network to handle various financial needs.

What is surprising about this forecast is that not a single voice challenged the predictions when they were made last week at a meeting of Robert Morris Associates, an organization of bank lending officers named for the Colonial financier who bankrolled George Washington's army.

Nor was there any serious disagreement among the executives who offered their opinions on the future of the banking: Robert F. Tardio, chairman of Suburban Bank of Bethesda; William Cowie, president of Union Trust Co. of Maryland; and C. James Nelson, president of National Bank of Washington.

Nelson, Cowie and Tardio are leaders of the new generation of professional bankers who now manage the region's bigger financial institutions. None of them owns the bank he runs; all became bank presidents by working their way up through the management of other banks before coming to the Washington area. They are old enough to understand where banking has come from and young enough not to fear where it is going.

When the revolution in local banking will come, they do not predict. The date depends on how long Congress can delay the inevitable and how well the financial industry manages the transition. It could take five years of trauma and bankruptcy or 20 years of efficient evolution.

How Union Trust, NBW and Suburban will survive the impending upheavel is another question the three executives do not answer. But not one of them blushes at the mention of merger or vows to remain independent forever.

It is a truism among professional bankers that there isn't an institution in the District of Columbia, Maryland or Virginia big enough that it couldn't be swallowed easily by one of the financial giants.

Some local banks are obviously on the block already. No one who watched Joe L. Allbritton's handling of The Washington Star believes he bought control of Riggs with the intention of keeping it forever. The First American Banks, on the other hand, are now owned by wealthy Middle Eastern investors who have neither the need nor the inclination to sell out.

A savings and loan franchise will be almost as good as a bank once barriers to inter-industry competition are lowered. Most every local savings and loan could be bought; Perpetual American is the exception, an institution determined to survive but not as an old-fashioned savings and loan.

As the barriers to interstate banking fall, Washington will be the first stop for Northeastern and Sunbelt banks moving into new markets. Some will come in search of affluent consumers, high-tech industries, government-related business. Others will want to be here just to hang out a sign on Pennsylvania Avenue and open a window on Washington.

Though Washington still has some of the most conservative (one could safely say backward) banks and savings associations in the nation, the region is simultaneously in the forefront of every financial trend: interstate banking, innovative services, industry consolidation, electronic funds transfer.

How those trends will reshape Washington's banking business is already becoming clear to the region's bankers