It is nighttime lockup, and all prisoners are supposed to be in their cells. A ''guard'' smoothly whirs his way down the halls, ''armed to the teeth'' with a complement of infrared, motion, sonar, and microwave sensors. His ammonia odor detector is designed to sense the presence and proximity of humans.
The robot prison guard constantly transmits its monitoring signals to central control points, and will sound a warning alarm if it is approached or attacked.
That's a scenario Sam Youngblood envisions. Mr. Youngblood, president of Southern Steel Company in San Antonio, Texas, hopes to market an intelligent metallic chap, guided by the the proper software, who could take his place along with human guards in many penitentiaries.
The robot will carry no weapon, and he won't be trained in karate - but Youngblood says it will sport a face that is deliberately crafted to look unfriendly. With a girth of 28 inches, it should be able to propel itself comfortably through a 30-inch-wide door.
Youngblood says the robot, which is still under development, could cut costs and eliminate the more boring, routine jobs that live guards frequently do not want to do. This could free the guards for more challenging tasks involving more personal supervision of inmates.
This is important, Youngblood explains, because one aim of corrections reform is to increase contact between guards and inmates. Ideally, the inmates should be broken up into smaller groups for more control. But that would require more guards, and many administrators are already short-handed and can't afford the expense of extra guards.
Youngblood says the use of robots for simple guard chores would allow live guards to spend more time with prisoners.
Yet Ken Schoen, a former director for corrections in Minnesota who is now with the Edna McConnell Clark Foundation in New York City, which funds legal action aimed at prison reform, says the effect could be just the opposite.
He is concerned that robots might further contribute to the impersonal atmosphere of prisons, where guards and inmates are already separated by devices such as remotely controlled door locks and TV surveillance.
''It seems best to normalize a situation, and this seems just the antithesis of that,'' Mr. Schoen says. ''I just can't imagine how this would work during nightly lockup.'' The only valid use he envisions for a robot is as an observation scout that would go into situations too dangerous for guards to penetrate.
Youngblood says he already has located a prison (he won't give the name) willing to experiment with a prototype robot by October or November.
Some prison administrators are skeptical. ''Somebody has got to show me it can work,'' says Rick Hartley, an assistant director at the Texas Department of Corrections. ''It would be very difficult for a machine to take the place of a human being's ability to detect and observe changes in tension or action on a cellblock,'' he adds.
In Woburn, Mass., the firm of Denning Mobile Robotics is working with Youngblood on an effort to design the shell and software for the guard robot.
A Denning spokesman says the target is to begin shipping out robots by February 1985. But he won't discuss the project in detail or allow photographs to be taken, partly on grounds that it might complicate patent applications.
Youngblood says Southern Steel already has an agreement with Denning to buy 200 a month for five years, once a satisfactory model has been developed.
He's hoping that the savings of the robot will be appealing. Hiring human guards to keep one person on patrol 24 hours a day runs $80,000 to $100,000 a year, he says. By contrast, one robot, costing between $30,000 and $45,000, will last 15 years, he adds.