NEW YORK >> Book your summer travel early. Don’t wait for huge sales.

This was the advice just a few months ago as airfares were rising. Demand was expected to be high and seats limited. Now the major airlines appear ready to give up some ground to penny-pinching travelers.

This is shaping up to be the most expensive summer ever for air travel. Fares could surpass the previous record average of $359 in 2008. But the airlines are growing nervous that higher fares will drive away passengers. So, those who dared to follow the traditional guidelines for booking summer flights are about to be rewarded with lower fares.

According to online travel site Travelocity, the so-called sweet spot for booking is generally six to seven weeks ahead of a major holiday weekend. By this model, airfares for July Fourth, for example, should fall starting around May 19 and go back up around May 25. After that, those fares should remain fairly steady until a week before the holiday. Then the airlines are likely to hit procrastinators with a 10 percent hike. This rule applies to Labor Day and other heavy travel weekends this summer as well.

Those who waited should do better than those who booked early for travel to many popular destinations, says Travelocity senior editor Genevieve Shaw Brown. Travelocity crunched airfare data from the last four years and found that booking more than seven weeks ahead of the Fourth of July cost travelers an average of $348 round trip, Those who waited until six weeks out paid an average of $326.

Why does this happen? While airlines are constantly adjusting fares based on demand and even the day of the week, they follow a few standard rules. They generally take stock of how many bookings they have on a given flight a month or two ahead of the travel date. If the plane isn’t full then, they want to fill it as soon as possible. That often means lowering prices to entice latecomers to buy.

Airlines successfully raised fares several times since December as oil prices rose to $113 a barrel. Yet three recent attempts to raise fares failed, and discount airlines started to undercut larger competitors by putting a limited number of seats on sale.

"They cried uncle," says George Hobica of airfarewatchdog.com. "Obviously they want to create a sense of fear — book now, book now, book now. But if fares are too high, people don’t fly."

You can predict a sale by looking at the seat map of your potential flight. Most booking websites offer a glimpse of available seats. If you see a lot of empty seats, expect a sale. But book as soon as possible if you see only a few empties.

Travelers who haven’t yet booked summer travel still need to do some research. Fare cuts aren’t likely to come in the form of flashy sales, and lower prices will often go unnoticed by those who haven’t been tracking fares.

A "deal" this summer is almost certain to cost more than it did in the last few years. Bing Travel predicts summer airfares will be 15 percent higher than last year. Even if oil prices do come down, airfares might stay high. If people continue to fly and pay more to do it, airlines have little incentive to lower fares.

Summer hotel rates are also expected to rise — by more than 7 percent. Hotels, like airlines, have slowed their growth plans and are now reaping the benefits of improving demand.

The cheapest airfares and hotel rooms will most likely come in a package deal, Travelocity’s Shaw Brown says. Packages allow airlines and hotels to fill seats and rooms without advertising bargain basement prices — they generally don’t break out the airfare or hotel room rate separately. But beware: Hotel rooms included in packages are sometimes not refundable. Airfares almost never are.

Still deciding where to go? Bing Travel says the cheapest summer destinations are Orlando, Boston, Denver and Las Vegas. Some fares to these locations have actually fallen since last year.

Despite higher prices, nearly 60 percent of Americans plan to travel this summer compared with about 50 percent last year, according to American Express. And more are planning multiple vacations.

Still, high travel costs are forcing travelers to adjust plans. More are opting for hotels with lower star ratings and booking shorter stays, according to data analyzed by Expedia. They’re also staying farther from city centers to get better deals.

American Express notes that 25 percent of people it surveyed plan fewer home improvements this year to save money for summer trips. Thirty-eight percent say they will dine out less and 30 percent will buy fewer clothes and move that money to the vacation fund.