Jacob Rabinow, arch inventor of Bethesda, has a daughter who is an assistant D.A. in Manhattan. Jean Ellen fled sobbing from the arena of invention at age 6, when the patent attorney broke the news that her device - an alarm notifying that the vacuum cleaner bag was full - had already been patented.

Her father knew the feeling. As an 8-year-old reading Jules Verne in Russian in Kustanay, Siberia, Rabinow invented a machine ("a couple of ropes with a stick in between") to throw rocks. Some adult told him the Romans had contrived that exact thing 2,000 years earlier. "I didn't know there were Romans," he said. "It didn't throw very well anyway."

In the threescore years since that disappointment, Rabinow has secured 210 American patents, most of them disappointments.

"Do you know the Second Law of Thermodynamics?" The one about spontaneous processes and total entropy? "No, Rabinow's Second Law is that There Is No Free Lunch." That means there is no perpetual motion machine except the phony model his colleagues presented him when he retired, and it has other ramifications, too:

"It means inventing is a hell of a lot of fun if you don't have to make a living at it. It means an inventor can get a job solving day-to-day problems; industry says, 'Fix it but don't change it,' so they don't have to re-tool. Do something new and people say 'It's different, but who needs it?'"

Rabinow has shelves of notebooks full of perhaps 2,000 yet unpatented ideas, but he doesn't have to make a living at inventing. He is inventor emeritus at the National Bureau of Standards, where he gave the right answer on March 24, 1938, when the man asked, "Do you like routine work?" The answer - "If I have to, I do it" - got him a job calibrating water meters and pressure guages for $2,000 a year.

He had no trouble leaving New York, where he had been living since his family escaped from Russia, via China, after the 1917 Revolution. When the Depression wiped out his mother's custom corset shop in Brooklyn, "Kuba," as she called Jacob, had to borrow the $62 tuition for graduate engineering school at City College, despite the fact that Happiness Furniture Stores raised him from $12 to $14 a week for his part-time job when FDR's NRA said they had to.

He had taken a "straight" B.S. at CCNY because he had been told repeatedly that there was no chance in America for a Jewish engineer, but when the corset shop failed, Kuba decided: "If I'll starve, I'll starve doing something I like." Having put together his first radio at age 11 and earned money during college wiring radios for twelve to fifteen cents apiece, he abandoned his compromise goal of being a teacher and switched back to engineering.

Rabinow retired in 1975 as Chief Research Engineer of the Bureau of Standards Institute of Applied Technology. He regrets having let it drop that he was at a pinpoint in time a millionaire, because that affluence was theoretical and ephemeral and people keep bringing it up. The occasion was his sale in 1964 of his Rabinow Engineering and Consulting firm to Data Control. In exchange for his forty-five patents on reading machines, incorporating a basic principle he discovered, Jake was made a vice president of the Rabinow Division and acquired stock worth more than a million. By the time he could sell it, Jake's stock had fallen to a third of its value.

"Look, I lost more than that on my photograph," he said. The Rabco, a record player the arm of which moves across the platter in a straight line, "the same way they're recorded," was a technical success, but Rabinow wound up selling it for a seventh of what it had cost him to produce it. Rabco is still a success in Denmark, where it is marketed by Bang and Olufsen; Rabinow receives no royalties because his 1954 patent, like all patents, expired after seventeen years. "But they invited me and Gladys to visit there," Jake said, "and it was nice."

Just say "Why doesn't somebody . . . " and Jake begins inventing it. A friend mentioned that he'd like to be able to read the label on a record while it was turning. Eureka: in Rabinow's playroom you peer through a hole in this little plywood box and read "Herb Alpert and the Tijuana Brass" while the beat goes on at 33 r.p.m. "Just a revolving optical system."

Different, as they say, but who needs it? "I never even gave it to my friend," Jake says. "It cost me $700 to make it and I fell in love with it."

Such costs are why inventing is usually done on somebody else's payroll. It is one reason why Rabinow, 68 "and counting" and a four-times-a-week tennis player, has only a half-dozen patents pending. "I'm working on a few gadgets," he said, "like pick-proof locks, which interest me like a puzzle." He doesn't know where his 210 U.S. patents rank him historically, "but Edison was supposed to have had 1,080, and Mr. Land of Polaroid, a superb engineer, has over 500."

There are always the disappointments, like Rabinow's headlight dimmer, which never sold. "It was the mid-1950s," he concludes, "and the [auto] industry wasn't interested in safety." But it is generally fun being the company inventor: "They tolerate some wise-guyishness from you." And there are great satisfactions.

"Hit one regulator in a lifetime," he said, "and you feel pretty damn good." The regulator came to be after Gladys, Jake's wife, gave him a watch in 1945 and it soon needed, like all watches, to be adjusted. Rabinow's regulator speeded up the action when the minute hand was moved forward - informing the watch that it had been laggard and must hurry - and vice versa. Clever, the industry said, but who needs it? "We advertise a perfect watch," said the Hamilton people. "Can we say it needs a regulator?"

Ultimately General Time, manufacturer of Westclox car radios, agreed to Rabinow's terms: $10,000 a year, three cents a clock. "The word got out, as it always does," Jake said, "and the companies that had refused it started calling. 'Where were you sons of bitches when I needed you?' I said." For almost twenty years the regulator brought in more than $20,000 a year, split 50-50 with Rabinow's patent attorney. "He used to say, 'Some guys play horses; I bet on Jake Rabinow.'"

There was gratification in 1948 in the six-page spread Life gave Rabinow's magnetic-particle clutch, invented in the service of the Bureau of Standards. It was one great step forward for the infant computer industry. "It was two metal plates with iron dust in between," Jake says. "Any kid could have invented it."

One result of such gratifications is the elegantly modern home Jake Rabinow had built "to order" in 1962. In it there is a sort of den's den that converts quickly into a dark room. "The guy who's building this," said a workman installing the plumbing, "must be some kind of nut. He wants two sinks, side by side, in his den."

"Yes, I know the guy," Jake told him. "He is a little crazy."