EXECUTIVE TRAVEL : Travelers Say They Feel Stiffed by Flier Program Changes : Airlines: Survey finds that more than 25% are angry. Most gripe about mileage requirements.

Business travelers are finding it easier than ever to pile up frequent-flier miles, but they’re increasingly unhappy about what they’re getting.

That message comes from a new survey that found that more than one in four people was angry enough about changes in the programs to reconsider participating in some of them.

Frequent Flyer magazine, which published the results of the poll, said most of the complaints involved new requirements that have raised the number of miles needed for a free trip and reduced the number of free seats available per flight.

“Frequent business travelers view their mileage points--and the associated free travel--as a reward for the hectic daily experiences they face continually on the road,” said Laurie Berger, editor in chief of Frequent Flyer.

“Even though a small amount of travelers surveyed in this year’s poll considered the changes in frequent-flier program fair business practice, the recurring message we heard was ‘Stop tinkering with our frequent-flier program,’ ” Berger said.

The explosion of non-airline gimmicks for racking up mileage--using certain credit cards, staying at certain hotels or buying certain products--has created a boom in mileage handouts. That, in turn, has made it harder to use the miles.

On top of that, recent waves of discounted ticket promotions have loaded up flights, meaning many planes have fewer seats set aside for freebies.

The number of free seats varies by airline, from no less than 5% to no more than 13% among the Top 10 carriers, according to Frank Dinovo, president of Travel & Transport in Omaha, the eighth-largest U.S. travel agency.

Based on complaints he hears from his customers, Dinovo said, there’s no doubt airlines have cut the number of free seats in recent months.

“I think that if this trend continues, you’re going to have a lot of people wondering if these programs are worth it,” he said.

Dinovo said about 75% of all frequent-flier miles are cashed in for upgrades by travelers looking for more comfortable seating.

“The airlines are tinkering with the whole concept,” said Michael Brent, president of Travel Network Ltd. in Englewood Cliffs, N.J.

He also said most carriers have lowered the cap on how many discounted or free seats can be justified on each flight. Only a handful may be allotted for people using mileage to fly free or upgraded, but if the plane isn’t full, a carrier will sometimes go beyond the limit and let more free or upgraded passengers on board.

The network of 334 travel agencies affiliated with Brent’s company have been offering a program in which travelers get mileage credit when they book through one of the agents.

The program is in addition to whatever mileage credit the traveler earns from the airline for the same flight, and the free tickets when earned come from the network’s inventory of bulk-bought tickets.

There are some catches, however, as a reader in California recently pointed out after an earlier report The Los Angeles Times ran on the program. For example, a cheap, non-refundable ticket earns only 50% of the air miles actually traveled. A full-fare coach ticket is needed to get the actual miles traveled credited in the travel agency program.

On the other hand, full-fare first class earns 150% of miles traveled, while full-fare business class gets 125%. Most companies that put business travelers in the air, of course, try to avoid paying full fare.

In addition, the travel agency program reserves the right to require a Saturday night stay on the tickets it hands out, since the tickets come from its own inventory and may have such restrictions attached. Information on the Travel Network plan can be obtained at (800) 222-2220.

Meanwhile, the November issue of Conde Nast Traveler magazine has a lengthy report on how some frequent fliers resort to fraud in mileage feeding frenzies that have become addictions.

Among the illegal gimmicks, the magazine reports, are scavenging airports and planes for discarded boarding passes and used tickets, then pasting in their own names and submitting them for miles. Another involves buying a refundable ticket, checking in to activate the mileage credit, then skipping the flight and getting a refund on the ticket, hoping the mileage credit sticks.