IT DOESN'T take a Harvard business school graduate to recognize that Cambridge is a haven for anyone engaged in the business of repairing automobiles. The streets are filled with mansized potholes, the traffic signals were designed by a little fellow who was paid off by the auto dealers and insurance companies, and three-fourths of the drivers are foaming at the mouth--consequently the accident rate in Cambridge is phenomenal.

The extent to which the repair business is thriving in Cambridge is reflected by the number of used part junkyards and body shops close by--the yellow pages list over 50 of them in Cambridge and Somerville alone. A sizeable number of these are clumped closely together in a three-block area along Columbia and Webster streets right on the Cambridge-Somerville line.

To some extent, a junkyard is a junkyard no matter where it is located. Yet, like almost everything in town, the Cantabrigian junkyard has some special features that distinguish it from the plain-old-ordinary-run-of-the-mill variety. Unlike the neatly piled, sprawling yard of rusted cars and buses depicted in the movie Nashville, or the mountainous heaps of uncategorized wrecks in the swamps east of Baltimore, or the medium-sized backyard and field lots of suburban Boston, the Cambridge yard is severely limited in size. Since the average junkyard here is no larger than a half-acre lot, the junkyard entrepreneur must be a master urban planner. Most Cambridge yards are arranged like a small, corner butcher shop--bumpers hanging along one fence; windshields neatly stacked on a shelf; alternators, starters and other "guts" in separate bins ready to be scooped out; and, some choice whole cars stacked to one side for "carving" up.

On a busy day, "Junkyard Alley"--as the Columbia-Webster streets district is nicknamed--looks like the Haymarket, with shoppers working their way from yard to yard, looking for the best quality and lowest-priced merchandise. Comparative pricing is as important in this line as anywhere else; experienced junkyard buyers know that prices on identical used parts may vary by 200 per cent in adjacent yards.

JUNKYARD ALLEY has a crew of regulars who match any pool hall or bar gang for devotion. Curb space along the side streets is often at a premium because these diehards use the curbs to elevate one side of the car so they can get underneath to do their work on the spot. And it's not easy to break into the select group who know the owners and always manage to get wind of the best deals and the latest tips on the wrecked 'Vette coming in tomorrow.

Most who wander into the alley are bewildered victims of the brutal ongoing warfare between Cambridge cars. If they're lucky, one of the yards will have a fender to match the make, model and color of the car; if not, the choice may be between a blue fender on a red car for $25 and a new blue fender for $125.

None of the operators are crooks but they don't exactly stress caveat emptor either. A smart buyer knows how not to get stuck with a bum part. Every yard on the alley will test any movable part upon request and most are proud to explain the special one-time guarantee--the part will be replaced free of charge if it fails to work up to and including the first time it is used after installation.

The owners and operators of the yards are the real characters of the alley. They cover the entire spectrum of stereotypes. There's the beer-bellied, loud-spoken bigot--"See that guy, he just got off. Happy as shit. Killed some fuckin' nigger the other day, runned him right over. Hadda go ta court today. We got 'im clean though; fuckin' judge lives right down the street from me. I spent Saturday afternoon over his house, lookin' at his car. Guy runned right over that nigger, but the judge lives down the street from me. Jeesus, he's happy..." And the bald-pated cigar-chomping businessman who looks like Kojak--"Gee son, I'm awfully sorry I can't let that one go for less than $25. I had to pay $200 for the car it came out of. I got the one for the V-6 cheaper, but the truth of the matter is I paid more for the one you need, so I got to charge more, you understand."

The high accident and attrition rate among Cambridge's automobile population is the lifeblood of the many junkyards on the alley--it creates a very high demand for used parts and it provides the dealers with an endless stream of junked cars from which to salvage those parts. The connection between all the cars piled in the yards in the alley and the personal injury and property damage that resulted from the traffic accidents involving these cars is often difficult to make. But, on some of the manged cars, cryptic yellow markings on the windshield tell the tragic story: "4-19-75. Head-On. 3 x'ed."

If Cambridge were a saner place, with half-logical traffic patterns, paved streets, and fewer rabid drivers, it could not support the scores of small junkyards it now hosts. But Cambridge is Cambridge, and the junkyards provide the best possible medicine for the victims of its driving maladies.