ON A PLEASANT treelined street in Rockville, lights burn late in the building out back of a trim red bungalow. A police cruiser slows at the sight of the lights, checks the address, then rolls on. The cop is used to the lights. They're a good omen. They mean Harry Stubbings has had an idea.

Ideas are the stuff of life for inventor Harry Stubbings, sometimes taking the place of food and sleep, even jolting him awake in the middle of the night. More often, they niggle him for days or even weeks before he finally pieces them together.

Harry Stubbings wasn't born to the lofty world of ideas. He was born to Alice Parmelee's English chauffeur and his French-Canadian wife. His childhood was made up of contrasts: one minute he was gleefully sliding down the snowy slopes of Tregaron, the Parmelees' Northwest Washington estate on Macomb Street. The next minute he was on his own in the world, a rebellious seventh-grade dropout.

But lack of education is no proof against genius, which ecperts explain as a genetic accident, a mutation unrelated to situation and circumstance: genius can't be fostered. Thomas Edison, credited with inventing the incandescent lamp and the phonograph, also had little formal education. He was expelled after three months in the first grade for being "dreamy and addle-minded."

While Stubbings denies that he deserves such a label ("I'm just a tinkerer, Miss"), he is very much aware that he shares certain characteristics with Leonardo da Vinci: the ability to write backwards, from left to right, for example. But whatever the label one gives him, Stubbings' gift is special, perhaps even more remarkable for having gone largely unrecognized, by him or anyone else, for thirty years while he earned his living welding sheet metal.

Once the ideas began, however, they came rapidly - and with results that may eventually make Harry Stubbings a wealthy man. After hearing about Stubbings from a local patent attorney and looking at some of his disclosure drawings, millionaire Charles Allmon created Potomac Applied Mechanics specifically to market Stubbings' inventions and to provide him with a $23,000 salary while he works on more. The U.S. Patent and Trademark Center has awarded Stubbings six patents since October. Applications for eleven more are pending.

At forty-six - clear-eyed, barrel chested, fingers thick as sausages - he is ready for success: "Sure I'd like to make some money. Wouldn't you? I've had to scratch all my life. It'd be nice not to have to worry about things." Not the "things" most of us would use new-found wealth to buy - his red house and Chevy pickup are fine, he says - but a bigger, more fully equipped workshop and an unlimited budget for materials.

Stubbings' inventions aren't the sort to tantalize the public's imagination - no electrical three-tined fork or sighing, heated toilet seat. They are, instead, refinements of existing processes and products, intended to save time, labor and production costs which, in the end, would save consumer dollars.

His first patent is for a circumferential welder, whose efficiency and labor-saving potential, he claims, would have made contruction of the Alaska pipeline less expensive. "I'm hoping they'll use it if they build those natural gas lines from Canada to the U.S. they're talking about," he says.

His other inventions include band and saber saws which cut in parallel lines, several other welding devices which he predicts will save money for the building trades, and a fool-proof lock and car mount for CB radios. He also devised, but has not applied for a patent on, a tiny balcksmith's forge which could retail for about $150. At present he is working out the kinks in a solar generator which homeowners could purchase for the price of a new car.

So far, none of the patents have been purchased by manufacturers, although an investment banking firm in Cleveland has agreed to undertake the selling of the welding devices. According to the corporate agreement, all of the patents belong to Potomac Applied Mechanics. As a principal shareholder, Stubbings will receive forty percent of all sales.

But despite the fact that large sums of money may be involved, Stubbings disclaims any interest in the business end of the venture, leaving those details to Allmon, himself an inventor and editor of Growth Stock Outlook, a financial newsletter, and to patent attorney Robert Vanderhye. "Harry has no grasp of the real world of common sense," says Vanderhye, "but he's brilliant."

Stubbings is content to climb into a clean set of work clothes of hundred feet to the cinder block shop he built back of his house ten years ago. There, behind a locked 260-pound steel door, he translates theory into substance.

Stubbings claims his ideas come from almost everywhere. He likes to visit local machine shops and just observe the equipment and the men working it."All I have to do is watch a machine for a while and I can figure out a more efficient one," he says.

He also finds inspiration in technical journals like the American Artisan, Design News and Machine News. Sometimes ideas come from reading the newspaper. That was the case with the circumferential welder: "I was reading about it [the Alaska pipeline] costing millions of dollars and all the faulty welds going on in the pipeline. So I read up on it, and researched it, and read some more, and checked into this and that. I thought to myself, why don't they have a welder that's going to do it right? So I drew the thing up. I also checked into a lot of big welding outfits and nobody had a patent on it. . .

"I know it will work," he adds. "You put eight of these [circumferential welders] at intervals on the pipeline. And they wouldn't cost that much to build. It would only take two men to run one of these and assemble it as well. That's a lot less money than paying all these ding-a-lings $1500 a week in Alaska . . . certified welders. And they didn't give a tinker's damn how they welded the thing. I was constantly reading about the leaks."

Like creative people in other fields, Stubbings works long hours, frequennntly staying up nights. He sees few people besides his wife Madeline and their four sons. "I feel I'm living in a vacuum and I'm a hermit," he says, "but that's the way I work best."

Part of the impetus to invent may come from an obsession with quality, which he traces to "just looking around and seeing a lot of shoddy work. I saw a lot of men doing inferior work. I also saw men getting paid for not doing any work at all."

Stubbings' first venture into improving quality was to build his sons first-rate toys. "I wanted my kids to play with toys that would last them for years," he recalls. "All I found in the stores was junk that would break in a week."

Those toys took on enormous proportions, both literally and figuratively. His magnum opus is an eight-foot-long, fully operational dump truck complete with blinking directional signals. He figures it took nearly 1000 hours and $782.11 to build the truck.

Starting out small by building a variety of three-foot trucks without many moving parts, he refined his "artist's eye" on those models. "All I need to do is look at something, say a truck is fifteen feet long, I think this should be so long and so high. I can scale with my eye without using a ruler," he says. What subtleties of design escaped his "eye" he found in books at the Rockville library.

As trucks proved less of a challenge, Stubbings turned to other things. He built a 300-pound, eleven-foot submarine in his living room, but had to dismantle it when his family complained that it blocked the way to the bathroom. An intterest in military weapons that began in childhood led him to build, but never fire, several full-scale rifles, among them some heavy machine guns and a French 37-mm antitank gun. His masterpiece during the artillery phase was a World War II German 88 cannon. It weighed seven tons.

Armaments still have powerful appeal for Stubbings, a gentle man who has never hunted or served in combat. He would like to include armaments in his inventing scheme and already has ideas for improving military models. "Weapons as machines fascinate me," he says. But the interest goes deeper than that: "And I'd just like to make sure this country stays on top."

He remains surprisingly unsentimental towards his creations. He keeps only photographs of a few of his favorite toys, and he has destroyed all of their disclosure drawings and working plans. He gave most of the toys away, either to children of friends or to the kids in the neighborhood. Now teenagers, most of the neigborhood kids bring him their souped-up cars for help in welding mufflers. They show their gratitude by leaving Stubbings' house conspicuously untouched on Halloween.

The seven-ton cannon went to the VFW Post in Rockville after Madeline pointed out it was difficult to mow the ggrass around such an object. And Stubbings sold his baby, the eight-foot dump truck, to a Baltimore family for $1100 after it won two first prizes in local car shows. He was sad to see the vehicle go, but the family needed money, he says, because the union at his shop had started cutting back his hours.

Although Stubbings says he had always gotten along well with his union, the Sheet Metal Workers, other, union members apparently grew fearful that improvements he had made on shop machinery would eliminate jobs. So, as Stubbings tells the story, they began to eliminate his job.

"First I received anonymous phone calls telling me to lay off my designs," he recalls. "I told them then and I told them later that just because a machine or process becomes more efficient does not mean men will be out of work. New machinery always creates new jobs."

Nevertheless, Stubbings' working hours were increasingly cut back - because of union pressure, the inventor charges. Fortunately, before the situation became too desperate, Stubbings met up with Charles Allmon.

That encounter and what grew out it changed many things. Ideas are no longer carried out merely to satisfy his curiosity or to provide something of better quality for his own use: "When I get my ideas mow I have to stop and think . . . Is this marketable? Is this economically feasible? What will Potomac Applied Mechanics think of it? . . . instead of just getting up and DOING it."

But he hastily adds, "I want you to know, Miss, I'm not really complaining."

No, it doesn't seem in his nature to be a complainer, nor a man who harbors secret fears. And if the burden of his gift grows heavy, or if he occassionally becomes awestruck by the uniqueness of it all, he's not letting on.

"I don't think I'm the greatest. I'm just a regular human being. I'm fortunate to have this knack. Lots of people are real swell-headed, but I'm not."

When pressed, however, he admits to occasional lapses.

"Oh, sometimes I wake up in the middle of the night and think, Good God, why me?" He sucks in a breath, places huge hands on wide spread knees. "Well, I don't know why me. But I'll tell you this, Miss. The good Lord gave me this gift and I mean to use it the best I can just as long as I can."