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

"I'd look at him and just say, 'I don't understand you!'" joked William P. Middleer Jr., one of five Gallaudet College students who began work last month as tellers when Riggs National Bank opened a branch in the school's Ely Student Union.

The new office will 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.

Although some banks have installed TTY machines to serve deaf customers, Robert Hileman, senior vice president in charge of the Riggs metropolitan division, said he knows of no other bank in the United States employing deaf tellers.

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

American Banking Association spokesman Daniel Buser said, "There are a number of banks employing deaf and mute people in computer jobs and other positions . . . but they are not out on the teller lines."

The City Bank of Dothan, Ala., has trained 13 of its 70 employes in American Sign Language to serve deaf customers, said ABA publicist Debra Bubb, "but I really haven't heard of any deaf tellers and I have a couple of 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 handled through sign language and lip reading.

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

For William Middeleer, 27, the program is a chance to break into the career of his choice. Middeleer was born with normal hearing, but a high fever when he was 10 months old left him deaf.

"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.

Middeleer's father is vice president of a Wall Street stock investment firm, Butcher & Singler Co. and, since childhood, Middeleer has yearned for a job in the financial sector.

"I had always wanted to follow in my father's footsteps," Middeleer signed. "He always told me, 'You can do it,' but you have to do so much talking on the telephone that I'd always been frustrated. But maybe if I can get a secretary who could translate, I could do it."

Middeleer, a native of Wilton, Conn., and Twila Turner, a 24-year-old Pennsylvanian, work full time at the Gallaudet branch. Carol C. Caragliano, 24, of New York City, Stephaine Hamilton, 21, of Lexington, Ky., and Raphael H. Glower, 22, of Kensington, Md., work part time, with their bank schedules tailored to fit their classes.

Riggs staff trainer Elaine Skelton, 26, and several other bank employes took a short course in sign language before the deaf teller class this spring. But Riggs and Gallaudet officials found that there was no signs for a whole list of banking terms such as endorsement, interest payment and mortgage.

"We have given the university a glossary of banking terminology and it has been developing signs for some of these phrases or words for which no signs exist," said John Stacey, Riggs metropolitan division vice president for personnel operations. "So there will be a contribution to the body of sign language growing out of this, too."

Riggs also used the Gallaudet students to test PLATO, a computerized teller training course developed by Control Data Corp., to the chagrin of some of the students.

"The course (extended to four weeks for the deaf students) was too fast for me. I tend to get lost in the maze of information," said Glower, a philosophy major who speaks intelligibly and is only moderately hearing-impaired. "Sometimes, when I got home, I had to sit back and say, 'God, please let me understand it all.' It's so much to learn."

Riggs spent about $80,000 equipping its leased office space, including designing several waist-high teller windows and installing an automatic teller machine with lowered controls for after-hours transactions by students confined to wheelchairs, said Hileman.

Of an estimated 206,000 persons with some type of hearing impairment in the metropolitan D.C. area, about 27,000 are totally deaf and could benefit from banks employing tellers proficient in sign language or other forms of deaf communication, said Brenda Rawlings of Gallaudet's demographic studies office. Nationwide, an estimated 14.5 million persons have hearing disabilities, close to 2 million of them living in total silence.

For Skelton, working with the Gallaudet students was enlightening.

"It's really made me focus on my communication with others," said Skelton, whose sign language name made up by her students means "smile." Working with hearing-impaired people, you have to be really expressive, which is something that I know now I wasn't in the past."

Riggs delayed opening the Gallaudet branch until summer, when most of the college's students are away, to give the new tellers a lighter customer load at first, said Hileman.

The bank is also employing several Gallaudet students in its data processing department this summer, and will have a deaf clerical intern at one of its branches.

"We have talked to the people at the college about using this as a springboard to get hearing-impaired individuals on a banking career path," Stacey said. "It's a little hard to tell at arms' length what we can achieve. But this experience . . . will give us some measure of what we can do with the hearing-impaired in banking."