C. P. Snow thinks the cultural gap in this country is between the sciences and the humanities. But in the city of Cambridge, the cultural gap is between Harvard Square and Central Square, and it is enormous. Central Square is the perfect example of a business center in a middle-sized American city: it is brash, noisy, ugly, vital and standardized. Harvard Square, on the other hand, is almost entirely the creature of Harvard University, and its commercial life is geared to the tastes and requirements of the University and its students.

The merchants of Central Square cater to the fundamental needs of life. Their stores, almost uniformly undistinguished, peddle the usual brands of food, clothing, furniture, and not a great deal else. Harvard people, as a rule, buy the bulk of their clothes at home and have their other necessities -- food, shelter -- provided for them by the University. So most of the things they buy in Harvard Square are, roughly speaking, luxuries. There are tobacconists, banks, bookstores, sandal shops, motorcycle dealers and bookstores.

If you have a taste for the unconventional or the bizarre, however, you can satisfy it in either of Cambridge's two big shopping centers. Harvard Square has Cardullo's, the Platonic Form of the Delicatessen. Central Square, with its lack of foreign affectations, has Central War Surplus.

Gastronomical Fair

Cardullo's, at 6 Brattle Street in the heart of the Square, is the Thermidorian reaction to Central Kitchen's republic of virtue. It is a year-round gastronomical world's fair.

Like everything else at Harvard, Cardullo's has a field of concentration, food, and it covers its field better than the Peabody Museum covers anthropology. If you are under the impression that food exists solely to fill that hole behind your navel, Cardullo's little tin cans and fastidious window displays will only annoy you. If, however, you think that food, even the sight of it, is one of life's more exquisite pleasures a visit might be worth your while.

Cardullo's comfortable interior is organized for browsing. Each area of the world has its own department, and in most cases the unfamiliar items outnumber the familiar. Still, however strange they look to American eyes, they are commonplace in the countries from which they come; few things are carried simply because they are odd. Cardullo's knows that that chocolate covered ants and fried grasshoppers -- those staples of run-of-the-mill "exotic" food stores -- do not a delicatessen make.

The place was founded back in 1949 by Frank N. Cardullo, who noticed that the delicacy counter at his restaurant, the Wursthaus, was doing enough business to justify a major investment. Mr. Cardullo prides him-himself on the variety of his pates de foie gras and the quality of his fresh caviar.

Passion Fruit to Betel Nuts

The selection is huge: tripes a la mode de caen and cassoulet toulousain from France, passion fruit and paw-paw from Africa, canned minnows from Poland, hearts of palm from Brazil, 180 different varieties of honey, and Scandinavian sardines packed in six kinds of sauce. There are instant coffees from at least a score of countries, including Hungary and Arabia; there are quail eggs and cuttle fish (a member of the squid family) packed in their own ink. And there are betel nuts, which, excepting coffee and tea, rank as the most widely used narcotic in the world.

Even John F. Griffin, the manager, doesn't know how many different items the store carries. "Several thousand, anyway," he says. "We feature more foods from more countries per square foot than any other store in the Commonwealth. We've built up our stocks through requests: if we get enough requests for something, we stock it." The increase in travel abroad has helped business. "People come back from India and want rice flour, so we give them rice flour."

Being in the foreign food business has given Mr. Griffin a somewhat larger world-view than most grocers. "We don't think of our food as exotic. What's strange to one person is a necessity to another."

100 Percent American

In contrast to Cardullo's cosmopolitanism, Central War Surplus, at 433 Mass. Ave., is one hundred percent American. Central was founded by former tech sergeant Ralph Glaser, who, with the help of a pair of dice, parlayed his army savings into an amount sufficient to buy a bunch of down sleeping bags from the Government.

Although it still carries the staples of any Army-Navy store, Central is in the process of changing over to sporting goods and sportswear. Most of the Government surplus is from World War II, and the supply is running out.

In odd corners of the store, among the T-shirts and sneakers, one can still find, for example, an anachronism like the first aid kit containing only a compress bandage and a package of shell wound dressing. Those with the inclination can buy sextants, litters, bayonets, shoulder holsters, jungle hammocks, gas masks and policemen's billies. Central no longer sells dog sleds, as it once did, but the suspicious purchaser in the market for a mine detector is its ideal customer.

Mr. Glaser views the increasing dearth of war surplus without much alarm. "I don't want any more wars," he remarks. "Someday I'd like to call this place Central Peace Surplus."