Special Holiday Fares Proving Popular : Airlines: Travel agents say demand is heavy--and the seats few--for $149 round-trip tickets to the East Coast.

Passengers were snapping up cut-rate airline tickets Wednesday after Delta Air Lines initiated a holiday fare war that allows passengers to fly coast-to-coast for $149 round trip--as long as they leave Saturday evening and come back Monday night.

The deal, which was quickly matched by other major carriers, is aimed at filling seats during the slack periods of the busy holiday weekend, a Delta spokesman said.

Travelers must depart after 6 p.m. Saturday and catch returns leaving before midnight Monday. The deal applies to most of the 155 destinations that Delta serves directly, including Los Angeles, Ontario and Orange County. It does not include cities that can be reached only by the airline’s commuter service.

Round-trip fares are $99 on flights up to 500 miles; $129 on flights from 501 to 1,000 miles and $149 on longer flights. The non-refundable tickets are good for only a limited number of seats on flights. Advance purchase is not required.

“The fares are offered in such a way as they don’t compete with our other fares,” Delta spokesman Clay McConnell said. “They fill seats that would go unfilled.”

Lee Howard, an airline economics consultant in Washington, said that even though airlines typically raise fares during the summer, when vacation travel is brisk, seats often go unfilled during the latter part of three-day holiday weekends. The late-Saturday-to-Monday offer is a way to remedy that.

Delta first tried such holiday discounts on Christmas Day last year. They were such a hit that the carrier repeated the offer for New Year’s Day. A similar deal on Memorial Day, McConnell said, brought the airline an additional $2 million in revenue.

Thom Nulty, president of Associated Travel Management in Santa Ana, said the fares are so low that they are drawing some people who simply want to ride in an airplane.

During the Memorial Day promotion, Nulty said, one of his travel agency’s clients flew to Chicago to have dinner with his mother and requested that he be booked on short-haul flights. “He even had a four-hour layover in Butte, Montana,” Nulty said.

Requests by travelers for the few low-fare seats available, however, have swamped some travel agencies.

Tami Truong, manager of Colby Travel in West Los Angeles, said she has had difficulty booking the cheap seats. “All airlines are sold out,” she said Wednesday afternoon.

Some potential passengers get angry, she said, when they learn how limited the promotion is. She had to tell one customer seeking a $149 round-trip ticket to New York that the next-cheapest seat available would cost $1,386.

“It’s not a good fare,” she said.