Most banking customers will never talk to a teller in the automated "mini-branch" opened yesterday in Georgetown by Union First National Bank of Washington.

The computer-run branch bank is the first of its kind in the Washington area, said a Union First official, and is a test run for further automation.

It hasthe same kind of outside 24-hour "money machins" used in 14 pair of faster, more sophisticated teller machines inside the office.

The machines, the bank's spokesman said, will handle virtually all personal checking account transactions. other Union First branches, plus a

The people in the branch will handle loan applications, commercial customers and more complicated personal account matters.

All customers of the automated branch, on Thomas Jefferson Street, south of M Street parallel to and between 30th and 31st Streets, N.W. will be issued plastic cards to activate the machines. The cards are optional with customers of other Union First branches.

Use of the automated teller machines will eliminate two human tellers and permit the branch to be housed in a much smaller building, cutting both labor and real estate costs, the Union First official said.

Including the cost of the teller machines, the mini-branch cost only about one third as much to open as a conventional branch.A major part of the savings was attributed to eliminating the vault and safety deposit boxes, the only service not provided by the smaller branch.

In addition to being cheaper, teller machines are supposed to be more convenient for customers because they can handle routine deposits and withdrawals faster than human tellers.

The major change for customers, the banker said, will be getting used to withdrawing cash in multiples of $25 -- the size of the money packets stocked in the machines.

While Union First is the first commercial bank to establish an automated branch in the Washington area, a network of automated teller machines are being used by a coalition of local credit unions.