Mailmobile - was winking and blinking down the corridor, the cousin of R2-D2 brought to Washington to facilitate the movement of paper. Robby had come to the right place.

A 700-pound device out of "Star Wars," Robby stands 4-feet-3, is 2 feet wide and 5 long, and moves at 100 feet a minute, slower than most people walk.

"We can catch up to it," said Thomas Zetty, chief, communications and transportation, office of administrative services and procurement, Commerce Department. He's becoming better known as the man who brought the robot to the federal governement, after he discovered it at a National Postal Forum at a local hotel. Robby now delivers the mail at Commerce.

Just then it stopped and chimed. "Sound like the Avon lady calling," said the woman, Marian Cairoli, who said her job was to "introduce the machine." Commerce has a stable of five, which deliver mail on the third through the seveth floors.

The General Accounting Office, the U.S. Geological Survey, the Department of Energy, and the National Science Foundation also own Mailmobiles, 250 of which have been manufactured by Lear Siegler Inc. of Michigan, a major government aerospace contractor. One had been running down the corridors of the Pentagon, an "unmanned, self-propelled vehicle's dream," It never got lost, but ran afoul of Pentagon security measures.

"The machine as now designed is not capable of handling classfied material, and half the mail at the pentagon was classified," said Lear Siegler's Douglas Mortenson, who thought up the Mailmobile. "So a mail messenger had to follow it around," guarding the open mail slots on either side.

These apertures add to the robot's odd appearance, which often causes double takes from passers-by. (A junior account executive with a New York company reportedly rode one like a horse when it first arrived.) "There's not as much reaction as you'd think," said Zetty, after a man glanced at it and moved on in the corridor. "We're in the age of automation."

After a 20-second pause, Robbt - some other users have nicknamed their machine Norman the Mailer, Remus (Reliable Expeditor of Mail U.S.), Archie Bumper - beeped and started up. Following an invisible chemical line applied to the floor, Robby with two flashing blue lights in front move around a corner and stopped in response toa perpendicular invisible line in front of a Commerce Department nursing unit. It chimed.

A nurse opened the door, took off maila and deposited mail. It then moved on to the Office of International Marketing, where another woman emerged. A few more feet and a man answered the chime at the Industry and Trade Administration.

"The first time I turned it loose," said Zetty. "I felt it wouldn't come back, but, sure enough, it does, like clockwork." It takes about an hour and 20 minutes to make the rounds, a presumably stops to talk. Robby makes five trips a day, always returning to the mailroom. At night, it gets its batteries recharged.

Zetty, who says an experiment is under way to equip one of the robots with classical music, likes the durability of Robby, who once was bashed by some movers carrying a desk through an office door. "It was only 'down' an hour," said Zetty.

One stop Robby doesn't make is at Commerce Secretary Juanita Kreps' office. "Her section is sectioned off by doors," says Zetty. "It wouldn't be cost effective to have someone open the door for it."