PROS, CONS OF SELLING NON-REFUNDABLE TICKETS ON `HIDDEN' MARKET

Bargain air fares may be nonrefundable these days - but that doesn't necessarily mean you'll lose money if you can't use the ticket. Stephen Bladen Douglas of Bowie, Md., purchased two such tickets last month for a trip to San Diego to visit relatives. But just before he was to depart, the friend who was to go along got a contract for the sale of her house, and the pair had to cancel the trip. They might have been stuck with the two round-trip tickets - and at $298 each, it would have been a considerable loss. Instead, they placed a classified ad in the newspaper and managed to sell the tickets for their asking price.

This "hidden market" in nonrefundable air tickets, as a spokesman for one U.S. airline has dubbed this use of classifieds, appears to be flourishing across the country. It is a phenomenon created by U.S. airline fare policies, and has appeal for both buyers and sellers: Travelers who can't use the nonrefundable tickets are delighted to be able to sell them rather than lose money, and buyers often can find bargains in the last-minute sales. A recent ad offered a round-trip ticket from Washington to San Diego over Labor Day weekend for only $250. Many nonrefundable tickets are sold among friends and business associates. But others are listed in the classified ads of community and college newspapers. Locally, The Washington Post and the City Paper regularly carry such ads, as do such other metropolitan newspapers as the Baltimore Sun, Philadelphia Inquirer and the Chicago Tribune. Some offers are for round-trip tickets; others are for one-way tickets only (practical for a college student heading back to school, for example).A recent Sunday Post classified section had about 60 individual ads, offering tickets to such diverse destinations in the United States as Boston, Boise, San Francisco, Los Angeles, Denver, Kansas City and Aspen. (The market in nonrefundable tickets is limited almost exclusively to U.S. destinations.) Not surprisingly, the airlines are unhappy about the hidden market - and do what they can to thwart it - usually by confiscating tickets they discover have been sold in this manner. The airlines assert that their tickets are not transferable, and thus selling a nonrefundable ticket is a breach of the contract under which it was originally purchased.

"We know this happens," says Neil Monroe, a spokesman for Delta Air Lines, one of four major airlines contacted whose policy it is to confiscate tickets.

"We do not approve of it," says Tim Smith of American Airlines. "If we find out about it, we'll revoke the ticket."