The country’s low-fare airlines are slashing prices for the busy summer travel season, an uprecedentedl step that underscores the weakening demand for travel.

Dallas-based Southwest Airlines cut round-trip prices on average of $70 to cities nationwide on flights through June 24, said Rick Seaney, chief executive of FareCompare.com, a Dallas-based travel firm that monitors ticket prices. Fares were as low as $49 each way, according to Southwest.

The fare sale includes flights to cities in Florida, the first time this year that Southwest has cut prices to those popular destinations. Sales this broad are rare for the summer months, Seaney said, because airlines traditionally can charge a premium for seats as vacationers flock to the skies.

AirTran Airways, an Orlando, Fla.-based discount carrier that serves Dallas/Fort Worth Airport, went further, slashing fares on many flights all the way through Nov. 4. The airline was offering service from D/FW to Orlando, for $84 each way. Some of AirTran’s prices are as cheap as $39 each way.

"I cannot remember the last time that an airline has given us this many travel days for a single airfare sale," said Tom Parsons, chief executive of Bestfares.com, an Arlington-based travel firm.

Most of the major airlines, including Fort Worth-based American Airlines, matched the sale prices on competing routes.

The airline industry is facing a weakened demand for travel amid the recession, as consumers tighten their wallets and businesses slash travel budgets.

Michael Derchin, an analyst with FTN Equity, said that low-fare airlines like Southwest, AirTran and JetBlue may outperform their rivals in a sustained downturn.

"We expect the low-cost airlines to be winners, as budget-conscious consumers have historically sought them out in recessions," he wrote in a note to investors Tuesday.