Business Notes AIRLINES

Perhaps the biggest headache for the airlines these days is a problem of their own making: frequent-flyer programs. Because of the carriers' competitive frenzy to hand out triple-mileage awards and other incentives, U.S. air travelers have racked up more than $300 million worth of free-travel credit. But now the No. 1 carrier, United, is leading what may become an industry-wide trend toward throttling back the giveaways. Last week the 4.5 million members of United's Mileage Plus program began receiving letters advising that the airline will launch a "new and improved" plan. In fact, the changes will impose much tighter restrictions on the most popular freebie trips.

United will actually lower the number of miles needed to get a free ticket (20,000 miles for a coach seat, vs. the current 35,000). But those tickets will allow travel only during certain times and within the mainland U.S. The airline will sharply increase the number of miles needed to fly at peak times to more desirable tourist destinations (a whopping 240,000 for two first-class seats to Hawaii, vs. the current 75,000).

The airlines are leery about reining in the programs because earlier attempts to do so provoked customer fury and threats of lawsuits. That is one reason United announced its plan so far in advance: it will not take effect until July 1, 1989. But now that the leading carrier has acted, analysts believe that several competitors will follow suit in a few weeks.