What would a deaf bank teller do if a pistol-packing bandit walked up to his window and shouted, "Hand over the cash!"?

"I'd look at him and just say, 'I don't understand you!'" jokes William P. Middeleer Jr., on of the five Gallaudet College students who began work recently as bank tellers when Riggs National Bank opened its new branch office in the schoold's Ely Student Union complex.

The office wil serve the faculty, staff and 1,500 students of the nation's only liberal arts college for the deaf, at 7th Street and Florida Avenue NW in the District.

Although some banks have installed TTY machines through which their deaf customers can communicate by typing, Robert Hileman, senior vice president in charge of the Riggs metropolitan division, said he knows of no other bank in the United States hiring deaf tellers.

With careers in banking all but closed to the deaf, many of whom are unable to speak intelligibly, the five Gallaudet students are breaking new career ground for the hearing-impaired.

The City Bank of Dothan, Ala., has trained 13 of its 70 employes in American Sign Language to accommodate its deaf customers, said American Banking Association publicist Debra Bubb, "but I really haven't heard of any good networks out across the country who know I'm looking for information like this."

While Gallaudet branch supervisor Gertrude Ghabel can hear, most transactions with the five deaf tellers will be communicated through sign language and lip-reading.

The five students were hired after a preliminary screening by Gallaudet's Office of Experimental Programs Off-Campus.

Middeller, 27, was born with his hearing intact, but a high fever when he was 10 months old left him deaf. His father is a vice president of a Wall Street stock investment firm, Butcher & Singler Co. and, since childhook, Middeleer has yearned for a job in the financial sector.

"Before I went to Gallaudet, one of my goals was to be in business administration," said Middeleer, speaking in sign language while interpreters Francis X. Burton and Janet Bailey translated for a reporter.

"I had always wanted to follow in my father's footsteps [as a stockbroker]. He always told me 'You can do it,' but you have to do so much talking on the telephone that I'd always be frustrated. But maybe if I can get a secretary who could translate, I could do it," said Middeleer, encouraged by his break into banking.

Middeleer, a native of Wilton, Conn., and Twila Turner, a 24-year-old Pennsylvanian, will work full-time at the Gallaudet branch. Carol C. Caragliano, 24, of New York City, Stephanie Hamilton, 21, of Kensington, Md., will work part-time, with their bank schedules tailored to fit their classes.