I discovered the painful truth when I recently needed to fly from Los Angeles to Chicago: There were no cheap fares. In fact, the ticket to Chicago was more expensive than a ticket to New York.

Then a travel agent suggested an alternative: She would sell me an even cheaper discount ticket to New York on a flight that stopped in Chicago. When the flight landed in Chicago, all I had to do was get off the plane.

I tried it. It worked. And I soon learned the practice was an open "secret."

I had used a "hidden-city" ticket -- a ticket written by savvy travel agents automatically (or after it's requested by knowledgeable clients) that gets travelers over large fare humps and other price hurdles by using false city pairs in order to obtain substantially lower fares.

In an age of increasing restrictions on airline tickets involving advance purchase, minimum stays and stiff cancellation or refund penalties, the hidden-city tickets are being written with greater frequency, especially for those travelers who need to fly at the last minute.

Hidden-city ticket writing is actually a long-standing travel practice, and as airlines have aggressively promoted their hub cities, using a hidden-city ticket has actually become easier.

For example, the current coach fare between Washington and Atlanta on Eastern Airlines is $218 round trip, based on 30-day advance purchase. But the advance purchase hidden-city ticket for a Washington-Chicago trip with a stop in Atlanta is $158.

* Other fare routings offer similar savings. A New York to Charlotte, N.C., fare can be much cheaper if the ticket is written New York to Miami with a stop in Charlotte. And hidden-city tickets are possible on even shorter routes. Passengers flying between Houston and Dallas have been saving money with hidden-city tickets written as Houston-Kansas City flights with a stop in Dallas.

On international flights, hidden-city ticketing can also save money. A ticket between Houston and Paris often is more expensive than a ticket between Houston and Geneva with a stop in Paris. A number of travel agents have been saving their clients substantial sums by writing the Houston-Geneva tickets and suggesting that their clients leave the plane -- as originally intended -- in Paris.

There are a few practical limitations for those who buy hidden-city tickets.

First, for obvious reasons, passengers should fly with only carry-on baggage. (If bags are checked for the flight they will be tagged for the ultimate official destination listed on the ticket, and they won't be put off the plane at the earlier stop.)

Second, the extra unused coupons for the unflown legs of the flight are more or less worthless. But passengers have been known to try to use those coupons. For example, a businessman who needs to fly to Denver buys a cheap round-trip Los Angeles-New York ticket with a stop in Denver. He, in turn, has a friend who needs to go from Denver to New York. When the businessman lands in Denver, he hands the ticket over to his friend, who continues on to New York. When the friend returns from New York, he reverses the process.

*Ironically, one of the reasons there are so many hidden tickets being sold is the competition between airlines. For example, if Continental Airlines promotes a cheap Los Angeles-Houston fare, other airlines, like American, will probably match it. However, American doesn't fly nonstop between Los Angeles and Houston. As a result, American will ticket passengers Los Angeles-Dallas-Houston (the same route, but with the added stop) and charge the same price as Continental's nonstop fare, which in some cases is cheaper than the straight Los Angeles-Dallas fare charged by American. (Obviously, you can't expect American ticket agents to suggest that you should choose this route instead of Los Angeles-Dallas direct -- but your travel agent might.)

American Airlines is not thrilled with this development or other ticket deals like it. "It deprives us of revenue and we consider it a breach of a business contract we have with either the travel agent and/or the passenger," says Steve McGregor, a spokesman for American Airlines.

"In some cases," he says, "we have no idea that the passengers are doing this. But when we discover a pattern, or in the case of the Fort Worth agency where they even promote it, we'll go after it."

Officially, airlines claim that the practice of using or selling hidden-city tickets -- or flying under someone else's name -- violates tariff agreements under which they operate -- not to mention that it reduces their income. It is not a crime for a passenger to buy such a ticket or give a portion of it to someone else to use -- though, in the case of a ticket's use by a person not named on the ticket, an airline could cite tariff violations and refuse to board the passenger. And sellers may face another problem.

Up until recently the airlines have made few efforts to stop the hidden-city tickets, but the current legal battle between American Airlines and Texas agent Jerry Weiner may be an indication of a new hard-line approach to the problem. American has obtained a court order and a preliminary injunction against two Fort Worth travel agencies owned by Weiner that had been advertising hidden-city tickets. Travel Management International and Wedgwood Travel were told to stop selling the tickets until the trial, scheduled for later this year.

"Sure, I promoted it," says Weiner, calling it "point beyond" ticketing. "It's a very common practice."

"Travelers want to go for the lowest fare," says Weiner. "I'm in business to get them that fare. Is it right that a passenger going from Los Angeles to Dallas pays more for his ticket than a passenger officially ticketed Los Angeles to Houston with a stop in Dallas? Given that choice, wouldn't you simply buy the ticket to Houston?"

A lot of people did. In preparing its case against Weiner, American Airlines audited two months' worth of his agencies' tickets and sent Weiner debit memos totaling $96,000 the airline claimed it lost because of hidden-city tickets.

"Their contention is that I cost them revenue," says Weiner. "My contention is that I put people on airplanes that otherwise would not have flown because the fares would have been excessive. A Charlotte to Denver flight with a stop in Dallas is much cheaper than a Charlotte to Dallas flight. The public needs to know this. I'm enjoying the challenge," he says, "and I'm actually looking forward to the trial." Weiner says he stopped promoting hidden-city tickets after receiving a warning letter about the practice that went to all travel agents on July 15, 1984.

Until the verdict -- and depending on what it is -- the practice of writing hidden-city tickets will most likely continue (with the exception of Weiner's agencies). "Sure it's a concern to us," says Chuck Novak, spokesman for United Airlines, "because it deprives us of revenue. But so far, we haven't pursued any travel agents on this." Airlines like United are waiting to see what happens in the Weiner case.

Not every travel agent enthusiastically embraces the hidden-city idea. If it reduces an airline's revenue, it also reduces an agent's commission.

"Still," says Weiner, "when the difference in fares can be in the hundreds of dollars, travel agents are being irresponsible to their clients if they don't write the hidden-city tickets."