THE TROUBLE with using chewing gum as coin of the realm is that it's hard to put it back into circulation once the flavor is gone. But that's just one of Italy's problems with small change.

The chronic shortage of "spiccioli" has long been a national joke and a source of aggravation for Italians and tourists alike. On my last visit I'd grown accustomed to receiving a stick of gum, a hard candy, an extra box of aspirin, or an apology instead of anything from 10 to 250 lire. The supermarket chain has long had a workable token system of red, yellow, green and blue tiddlywinks ranging from 5 to k 50 lire, good only at their stores.

This August, when my family and I returned to Italy after four years, I discovered yet another development in the struggle to make change.

We were heading north on Autostrada del Sole and turned off at the exit for Florence. As our rented Flat 124 grumbled to a halt at the toll booth, I dived in amongst sleeping children, backpacks, suitcases, six years of art historical research notes, an eighth size Suzuki violin, and a plastic bag of fruit, emerging triumphantly with a crumpled 10,000-lire note we'd changed before leaving the States.

I handed the bill to my husband, who passed it through the window to the attendant. The attendant handed back our change. We stared. We had never seen bank notes like the ones we'd just received. Mystified, we drove slowly away from the toll booth.

The bills were labeled with denominations such as "50" and "100" lire, which we knew ought to be coins. Furthermore, we had serveral of the 100-lire notes, and no two were alike.

We drove on to the apartment we'd rented, unloaded, returned the car to Hertz and settled down to critical marketing (mineral water, shaving cream, mosquito repellent). In the process, we learned more - much more - about the current crisis of Italian currency.

About a year and a half ago, utterly frustrated by the lack of coins for change, enterprising banks began printing their own paper money. These originated as "circulating checks," with 50-, 100-, or 200-lire denominations issued by the bank and redeemable at that bank for "real" money. At first, people were suspicious of these checks, but the bills gradually became so well accepted that they took their place amid those printed by the government as legal tender.

So it was with us. When we saw that these diverse little bills would buy our morning capuccino, a Joaf of Tuscan bread, or a kilo of stsring beans, our reluctance to accept them diminished.

According to the director of a Florentine shipping firm, the bills are actually cashier's checks, which should be signed at each transaction and are only legal for six months. In fact, six months after their initial appearance, a judge declared the circulating checks illegal. Another judge subsequently overturned that ruling - or something like that - concluded our shipping friend. In fact, no one seems too clear about the precise legal status of these bills, but that hasn't affected their circulation in the least.

Somehow, the development of a viable money system here seems, like any successful fiction, to depend upon the beholders' willing suspension of disbelief. Admittedly, it is like participating in an elaborate charade, but the rules of the game have been defined and accepted and the system works. According to the rules, a "gettone" (telephone slug) may properly be put into play un place of either the 50-lire "check," and at certain establishments where stamps are sold (post offices, bars, stationary shops) stamps themselves may pass either way over the counter as legal tender. Well, as tender, anyway.

I suppose I should be content with this solution. After all, things could have regressed all the way back to the barter system, and it's doubtful that the greengrocer would trade us peaches and pears for a book review or that the butcher would hand over a good cut of stewbeef after being refreshed with a lecture on 15th-century, Ferrarese art.

Still, the small-change bills have their drawbacks. I miss the 50-and 100 lire coins that are so rarely in evidence now. They have that sort of solide heft and gratifying ring that would warm the heart of a Scrooge McDuck (a kind of national hero here, where comic-book reading is not confined to children). I know the bills are easier on my husband's pockets and lighter in my purse, but it gives a peculiar feeling to send our 3-year-old off for his 30-cent ice cream cone clutching three paper bills in his hand.

Ironically, since our last stay, buses have changed over from ticket-sellers seated at the rear of the bus to automatic ticket-vending machines. These machines will only accept 50-and 100-lire COINS. The only way to play it safe is to buy an 11-ride punchcard sold at neighborhood stores, and ignore the machines that are becoming obsolete only a few years after their inception.

The greatest inconvenience of the system, though is its diversity. One never knows what the next 100-lire will look like, so counting our change is time-consuming.The same sort of careful scanning is necessarry when trying to add up a sum from one's own miscellaneous collection. Each issuing bank has its own designs for each denomination, and the bills may differ in size, color and the position of the critical value. The innovation must have been a boon for Italy's graphic artists, but they obviously embellished the bills with a great deal more zeal than good taste or concern for functional design. The 100-lire check is issued by the Istituto Centrale delle Banche Popolari Italiane, for example, sports a pink, light blue and brown color scheme, its four "100's" resting against a dizzying background of minuscule brown leaves. Tiny words and figures disappear in floral swirls that look like the work of a Spiragraph. On the reverse side is the bank's seal (blue) and some barely discernible because the bills, printed on flimsy paper, are quickly reduced by use to a soft, pulpy consistency.

The flimsiness and inconsequential value of these bills has caused a good many to blost, thrown away or destroyed (an American acquaintance confessed to having lit a cigar with one). As a result, the issuing banks are millions of lire the richer.

The problem of easily recognizable currency has not been aided by another development since my last visit: Three new bills have been issued by the government itself: a 20,000-lire note, a 2000-lire note and a new design for the 500-lire note. Imagine the frustration of sorting through a wide variety of small-change notes, two types of 500-lire notes, a 1,000-, 2000-, 5000-, 10,000 and 20,000-lire note and still having less that $45 to show for the effort. And to think that we had so much trouble accommodating the $2 bill!

The amibale proprietor of a stationery and toy store explained another wrinkle in the situation. The circulating checks, issued by banks all over Italy, each offering unique designs, have become collector's items. The stationer explained that in addition, there are counterfeit issues of some of the circulating checks and far from being worthless when discovered, these are even more valuable that the genuine checks - as collectors' items.

The stationer himself assured me that he was not a collector. Nor was he eager to accumulate the ciruclating checks. He showed me how he kept two change boxes under the counter, one with the paper change, one with coins. When customers passed him paper, he passed them paper in return. If someone insisted on coins, he took out the other box to make change.

He also had an explantion for lack of metal coins (arising from the sort of hoarding he and probably the rest of Italy is doing, i.e., put the coins in your piggy bank and pass the paper to the butcher). The government minting machine was missing for a while (missing?), but now they have a new one and can begin to make more coins.

The director of our local branch of the Cassa di Risparmio had a different explanations. He said the government had previously delegated the minting to a private concern but was now taking over the operation. The transition caused a slowdown in production. "It's the government's fault," he explained. At least that takes the onus off Italy's tourist population, long accused of carrying off the coins in their pockets. Unfortunately, that's an incontrovertible charge. Banks will not convert spiccioli back into foreign currencies, so the coins go back home as souvenirs or "play money" for the children.

According to our shipping-director friend, the coin machines are neither missing nor in private hands. The old machines, government-owned, simply couldn't keep up with demand.New government machines were being made. The owner of the local delicatessen agrees. However, he laments, even with the new machines, the government can't get the coins into circulation fast enough. He blames the tourists and, in addition, the vending machines, claiming that the coins swallowed up by bus-ticket machines or cigarette machines don't return to circulation for at least six months.

I called the Bance C. Steinhauslin & C. for further enlightenment. The voice at the other end of the line voted with the man from the deli ("It's the vending machines"), but the reason he gave for the new minting machines not being able to keep pace is that they haven't gone into production yet. "Next Fall," he said. "September of October." We'll see.

Stopping in at the imposing Banca Nazionale del Lavoro under the heavy arcade that backs the Piazza della Republica, I tried to pin down one of the tellers about the circulating checks. "They're just the same as money," he replied. He hastily added, "Of course you don't have to accept them if you don't want to." I asked what would happed if the government took them out of circulation, declaring them definitively illegal. Would those remaining in private hands be worthless? The teller leaned forward and lowered his voice conspiratorially. "You've got a lot of them?" I admitted I hadn't. "Well, then . . ." He dismissed me with a shrug.

I got the point. If the system works, and I haven't invested heavily in it anyway, why should I care how it functions or where it's headed? It's just my lack of Latin blood that makes me hunger for logic and efficiency. Still, if all those enterprising banks printing up their own money would only come to some accord about a standardized, color-coded system, petty economic transactions would be immeasurably simplified.

It's not as though the banks have no one to turn to. Surely, for the appropriate consulting fee, experts in the field would design and or print a color-and-size-coded system convenient to all. Of course, one could argue that this is precisely the role of the national government. Italian governments, however, are never around long enough to gain much expertise in any given field, and while they've done all right with the larger denominations, they don't seem to be equal to the problem of small change. Personally, I'd award the monopoly to Parker Brothers.After all, they've been in the money-making business for decades.