A hefty envelope bearing two brand new VISA cards arrived in the mail the other day. This wouldn't seem significant under ordinary circumstances, but let me go on.

As the family bill payer, it is my job to toss the daily batch of coupon packets, prize sweepstakes, charity appeals, real estate newsletters and assorted advertisements and to file the bills.

I usually put off opening the bills until just before due dates, but on this particular day I did look at the VISA bill. A $600 charge leapt off the page with a force all its own.

What has he done, I wondered, immediately casting all blame in my husband's direction. He used the card for business expenses, but the total rarely topped $200. This charge was for a $600 Western Union money order.

A call to his office cleared him and created a puzzle. Indignation rising by the second, I typed out a letter to the address listed on the back of my card under "credit disputes."

"This is not our bill," I wrote. "This item is an error. Please correct immediately."

It was short and cryptic and so was VISA's return post card which noted the disputed amount and advised us that it would be credited to my account until "final resolution."

The resolution arrived two weeks later. We were obligated to pay VISA the $600 because (a check in the box here), "proper identification was on statement."

The clincher was a photostat of an unsigned sales draft for a money order issued in Las Vegas, Nev. I could see it all. Slot machines, blackjack tables and Wayne Newton--all paid for at my expense.

Feeling powerless to fight VISA's ultimatum alone, I called the Better Business Bureau. They classified me as a victim of fraud and advised me to call the police.

My phone conversation with the county fraud division did much to alleviate my '60s prejudices against uniformed authority.

"Those bastards," exclaimed the policeman as soon as he heard my story. "People commit fraud with credit cards all the time. Go to the bank and get an affidavit of fraud and send it through certified mail to VISA.

"And," the policeman added ominously, "be sure to run a credit check in six months. If they have given you a bad rating, sue them."

The next letter to VISA went out on my husband's business stationery, which prompted quicker reaction than my home-typed note.

This time it was a phone call from Nora at our out-of-town VISA bank. Once I had convinced her that I could handle the situation--and that she needn't call my husband at work--she spewed out directions. We were to cut up our VISA cards, mail them to her and fill out a battery of questionnaires.

Every few weeks brought more correspondence. New cards with a new number and a six-month expiration date were sent by registered mail along with the warning, "We will attempt to arrest any person using your previous account."

Clearly, things had gotten serious. And then Novack, our VISA investigator, called. Together we examined the evidence. I had made a phone order using my VISA account shortly before the "disputed charge." Or, possibly my account number was picked up by a cashier during an in-person transaction.

Novack wanted to know if anyone had called to verify my account number. He was also suspicious of racetracks and companies giving cash for a fee and a credit card number.

"We look for a pattern," said Novack. "If more than one disputed transaction originates at the same location, we investigate."

Novack was less than subtle in probing my credibility. "So," he asked, "and what does your husband do (information the credit card company surely had)? And where was your previous address?" We closed with a discussion of the weather.

Then, a clue arrived in the mail. Feeling like a one-dimensional character in a detective paperback, I examined the Las Vegas return address. It was a marketing solicitation letter, but obviously, I decided, it was part of the pattern we were looking for.

I called Novack, and he promised to investigate, adding that these things take time to resolve.

A lull of several weeks passed between that call and the arrival of a second set of new cards. No suspects have been apprehended, so far as I know, but we are apparently back in a good credit rating. Our new VISA cards do not expire until 5/83.

Betsy Brooker is a free-lance writer.