After our first two robberies last year -- my husband's at gunpoint as he walked home from work, and mine a purse-snatching at noon in a residential neighborhood -- I felt certain I had learned all there was to know about dealing with robberies.

For months I dined out on my expertise, eagerly imparting to every willing ear my systems for quick and easy replacement of any item that could conceivably be carried in a wallet or handbag. You name it, we had lost it.

But then it happened a third time, and I learned that problems are quite different when you're robbed in a strange city, and on a Sunday.

I was in New York City, having stopped just for the weekend on my way to a family celebration in the western end of the state. I was robbed in my hotel as I walked to the coffee shop. The route leads from a busy lobby through an enclosed area with solid doors at both ends, and there is no video system or any other protection for hapless guests who enter the trap.

It took only an instant for the thief who lay in wait to peel my handbag from my shoulder and vanish through the other set of doors. Gone was all the cash I had brought with me, plus travelers checks, credit cards, driver's license and air tickets.

I consoled myself. It could have been worse. I wasn't harmed, and the travelers-check people are famous for quick relief. Maybe I could still make that day's plane flight.

After reporting to the police, I set about covering my losses. I immediately called the toll-free number Visa issues with its travelers checks and reported the serial numbers (safely tucked away in my luggage). After several minutes of answering questions -- we had just gotten to my age, height and color of eyes -- I asked how soon I could get the cash I needed today.

Today? Sorry, today was out. I had lost all my identification and without it my lost Visa checks could be replaced only by the bank that issued them. If I would phone the bank tomorrow (I found out it was in Chicago) and tell them my story (and presumably answer the same long list of questions) they would be able to take care of me.

I did not leave New York that day. But I could have, had I known a few more facts. Never let anyone tell you it can't be done on a Sunday.

If I had been carrying American Express, BankAmerica or Citicorp travelers checks, I would have been able to secure at least $100 to tide me over until the next day. On Sundays, American Express directs customers to the Nearest Holiday Inn for partial reimbursement, and BankAmerica and Citicorp use Western Union to transfer funds. It may take awhile -- sometimes two or three hours according to a spokeswoman for American Express, because other persons must be contacted to verify your identity -- but it can be done.

It didn't lift my spirits at all to learn sometime afterward that some issuers of Visa checks (there are 32 in all) do allow Visa to act for them during nonworking hours.

"We are simply a coordinating entity," says Visa Vice President Vincent Lapaglia, explaining that the issuer sets its own requirements. In my case the issuing bank insisted on "paper identification" as a requisite for a Sunday refund. It was the luck of the draw, and I had missed.

Another way of getting cash is by having someone at home wire it. In the absence of adequate identification, Western Union pays on receiving the correct answer to a test question you have arranged with the person forwarding the funds. Western Union offices are open round-the-clock in larger cities and part of every day, including Sundays, in medium-size cities.

Sometimes even faster service is available through the Travelers Aid Society. For this venerable social service agency, which has been helping travelers out of predicaments for most of the 20th century, Sunday is no problem. They telephone your distant friend or relative and direct him to the closest Travelers Aid office, where he hands over the money. That office phones your Travelers Aid to confirm the transaction, and the same amount of cash is placed in your hands.

Canceling credit cards is a tedious process any day of the week, but someone else may do it for you. As a service to its travelers-check customers, American Express cancels all lost or stolen cards, and even sends you a written confirmation listing all cards canceled. Visa, I am told, is supposed to ask if you would like your cards canceled; I can only report they did not do so in my case. BankAmerica introduced its card-canceling service in February. Citicorp does not offer this service but is considering it.

If you have been lucky and your credit cards have not been stolen, remember that most major issuers have cash-advance systems. Visa and MasterCard allow you to draw sums up to your available credit limit; American Express lets you draw on your own checking account. Basically that's a workday activity and might not help you if you need cash on a weekend.

While you are drawing your supply of dollars, include enough to cover air tickets and a lost-ticket reporting fee of up to $25, depending on the airline. You cannot report a loss by phone because you must fill out a form; if it's a Sunday it means a trip to the airport. Reporting the loss protects you against unauthorized use of the tickets, but refunds are made in the form of credits to your charging account. Meanwhile, you must purchase new tickets.

One exception to this rule is TWA, which says that its computereized system, in which all tickets are recorded by number and place purchased, can replace your tickets in a matter of hours, free of charge, except for a $25 reissue fee. TWA would need your ticket number to provide this service, so it would be wise to record it and keep it separate from your wallet or purse.

I probably worried more than most people would about my missing driver's license. Happily, the law is more understanding that I realized. So long as it is on record that you have requested a replacement, you may drive with an easy conscience. I simply phoned my local motor-vehicle bureau (Washington, D.C.) and asked that a replacement application be sent to me at my visiting address. Had my license been issued in New York State, I could have gone to any state motor vehicle office, paid $3, and a duplicate license would have been mailed out the same day.

The major hurdle for any traveler in a robbery case is proving who you are.

"You can usually identify people to your satisfaction with just a few extra questions," says a TWA spokesman. "We have to do it more often than you'd think."

Usually the personal information sought is the kind that strangers could not know, such as your mother's maiden name, the birthdate of another family member of physical identification -- scars, birthmarks, and the like. This is then verified by a third party.

Not surprisingly, airline, bank and credit-card spokesmen are hesitant to reveal too much about this intricate procedure, but they left no doubt that identification is always possible, provided the persons involved make a serious attempt. CAPTION: Pictures 1 and 2, The shoulder cache, $10, and the money belt, $6.95, are among "travelers' caches" available at area stores.