United Airlines launched its "Mele Kalikimaka" fares yesterday, knocking about 30 percent off the cheapest previously posted fare.

American, Northwest, TWA and Delta matched and other airlines were likely to do so to remain competitive.

United started the holiday fares in 1984 as a way of filling seats to the mainland on return flights after the aircraft leave mainlanders in the islands for the season.

In recent years the airline has put the fares into effect without fanfare, as it did this time.

Examples of the cheapest round-trip fares for off-peak travel (Mondays through Thursdays) during the season are $683 to New York, down from $957; $674 to Chicago, down from $940; $390 to San Francisco, down from $537; and $370 to Los Angeles, down from $537.

United said the fares are good for outbound travel from Hawaii Dec. 19 through Dec. 29 returning Dec. 29 through Jan. 7.

There are no prohibited days providing travel is between those dates, the airline said.

To qualify for the cheaper fares, travelers must produce proof of Hawaii residency such as a driver's license or other local identification.

The tickets are for purchase only in Hawaii and travel must originate in Hawaii. Reservations must be made at least seven days before the trip and the tickets have to be paid for two days after the booking or seven days before travel, whichever is first.

The tickets are not refundable and there will be a $100 charge for changing the return flight after the ticket is purchased.

The Christmas fares are available only for some seats on each flight and the airlines are advising people to book early.

Most of the airlines had the new fares in their computer reservations systems yesterday.

The filing of the Christmas fares came just after the airlines ended a fall sale that included mainland-Hawaii fares.