Northwest Triggers Another Air Fare Battle : Airlines: Rivals say they’ll match the carrier’s 2-for-1 offer. The offer puts the price of an L.A.-New York round trip for two at $643.

In the latest in a string of fall discounts, Northwest Airlines hatched a domestic 2-for-1 air fare sale Tuesday that cuts the price of a round-trip flight from Los Angeles to Chicago to $569 for two. The deal was matched by many major carriers.

The promotion, offering discounts of 50% for two people traveling together, are in line with a series of previous reductions this fall that have routinely cut the price of a round-trip ticket to the East to less than $400. Like the previous sales, the Northwest offer requires 14-day advance purchase and travel between Oct. 11 and Feb. 15.

The Northwest deal would let two people fly from Los Angeles to Miami for $628 and to New York for $643.

A round trip for two from Orange County’s John Wayne Airport to Detroit would be $575. Tickets must be purchased by Friday, and lesser discounts are available for international travel.

The deal is not available during popular travel days near the Thanksgiving and Christmas holidays.

Major airlines--including American, USAir, Delta, Continental and America West--said they would match the Northwest offer on routes in which the carriers compete.

In addition, America West announced a new phase of its discounting with reductions of up to 52% to selected cities.

Travel agents said the newest discounts appear to be a response to consumers’ expectations of lower prices.

“There are so many of these popping up one right after another,” said Dianne LaPorte, vice president at World Travel in Santa Ana. “They are becoming the norm rather than the exception.”