Lucrative Air Route to S.F. Sparks Fare War : Airlines: Competition and more flights reduce price of round-trip ticket to $58 on popular flight.

An old-fashioned summertime fare war is heating up in the busy air corridor between the Bay Area and Southern California, and passengers who plan ahead can expect bargains.

Major airlines flying between any of Northern and Southern California’s airports last week began offering $58 round-trip fares, the lowest in several years. United and USAir began offering the reduced fares early in the week, with Delta, American and Alaska following suit after the Fourth of July holiday.

“Travelers are going to have a break for a change,” said Ralph (Bud) Conner, an El Monte travel agent and vice president and secretary of the American Society of Travel Agents, a trade group.

To be sure, the cheap seats carry some stiff restrictions. Customers must buy the tickets 21 days in advance, and the number of low-fare seats will be limited. The tickets are non-refundable and do not cover Friday and Sunday departures. But passengers wanting to fly on a Friday or a Sunday may pay $34 each way, for a $68 round trip.

The lower prices offer a reprieve to the steep fares that have caused grumbling among passengers even as airlines have stepped up the frequency of flights in the corridor. Tickets bought at the last minute still cost as much as $186 each way.

A Los Angeles-based spokesman for UAL Corp.’s United Airlines said increased competition in the lucrative California corridor sparked the fare war.

Southwest Airlines, based in Dallas, recently entered the market with $58 round-trip flights between Oakland and Burbank or Ontario. On July 1, USAir began its California Shuttle, offering hourly service between San Francisco and Burbank. The airline also has hourly flights between Los Angeles and San Francisco.

In addition, American recently went back to hourly corridor service after having cut back for a time. And Delta entered the market with hourly service on June 1.

United now has the most flights in the corridor, with service every half-hour between San Francisco and Los Angeles, the most popular route. It has 120 flights each business day between the Bay Area and Southern California, up from 38 in 1988.

Until this latest round of price-cutting, airlines had been wooing customers with such services as more convenient gates, free newspapers and coffee. United also last month began awarding its frequent-fliers triple mileage for flights between San Francisco and Los Angeles.

Such $58 round-trip fares have occasionally been offered on less frequently used routes, such as San Jose to Los Angeles and Burbank to Oakland. But Angel Cruchett, with Associated Travel in Santa Ana, said she has not seen such widespread discounts in several years between the Bay Area’s three airports and Southern California’s five airports.

She said that she has had “a few bookings” for the low fares but that most of her clients--business travelers--generally cannot take advantage of them because of the restrictions.

Agnes Huff, a spokeswoman for USAir, said pricing officials at the airline have no idea how long the cut-rate fares will be in effect. Fare wars tend to generate business but cut into profits.

“Obviously, they can’t last forever,” she said, “although I’m sure the customers would like them to.”