Now, the shift toward developing smaller, lighter and less expensive systems is unmistakable. Supporters say it is a consequence of the effort to cause fewer civilian casualties. The Predator aircraft, for example, is being equipped with smaller, lighter weapons than the traditional 100-pound Hellfire missile, with a smaller killing radius.

At the same time, military technologists assert that tele-operated, semi-autonomous and autonomous robots are the best way to protect the lives of American troops.

Army Special Forces units have bought six lawn-mower-size robots — the type showcased in the Robotics Rodeo — for classified missions, and the National Guard has asked for dozens more to serve as sentries on bases in Iraq and Afghanistan. These units are known as the Modular Advanced Armed Robotic System, or Maars, and they are made by a company called QinetiQ North America.

The Maars robots first attracted the military’s interest as a defensive system during an Army Ranger exercise here in 2008. Used as a nighttime sentry against infiltrators equipped with thermal imaging vision systems, the battery-powered Maars unit remained invisible — it did not have the heat signature of a human being — and could “shoot” intruders with a laser tag gun without being detected itself, said Bob Quinn, a vice president at QinetiQ.

Maars is the descendant of an earlier experimental system built by QinetiQ. Three armed prototypes were sent to Iraq and created a brief controversy after they pointed a weapon inappropriately because of a wire connection failure.

However, QinetiQ executives said the real shortcoming of the system was that it was rejected by Army legal officers because it did not follow military rules of engagement — for example, using voice warnings and then tear gas before firing guns. As a consequence, Maars has been equipped with a loudspeaker as well as a launcher so it can issue warnings and fire tear gas grenades before firing its machine gun.

Remotely controlled systems like the Predator aircraft and Maars move a step closer to concerns about the automation of warfare. What happens, ask skeptics, when humans are taken out of decision making on firing weapons? Despite the insistence of military officers that a human’s finger will always remain on the trigger, the speed of combat is quickly becoming too fast for human decision makers.

“If the decisions are being made by a human being who has eyes on the target, whether he is sitting in a tank or miles away, the main safeguard is still there,” said Tom Malinowski, Washington director for Human Rights Watch, which tracks war crimes. “What happens when you automate the decision? Proponents are saying that their systems are win-win, but that doesn’t reassure me.”