Anyone who has ever circled a crowded parking lot looking for an empty space has got to envy Gwen Windham and Michael Griswold.

The Baltimore couple drove to Reagan National Airport yesterday to catch a flight to Alaska, only to discover signs near the entrance announcing that the economy lot was full.

Deciding to give it a stab anyway, they drove to the lot ready to pounce on any space a departing driver was vacating. Instead, an attendant at the entrance directed them to the more expensive garages across from the terminals and handed them a voucher entitling them to pay the remote lot rate of $9 a day.

"It could have been really bad," said a pleased Griswold as he unloaded luggage from his car in a $15-a-day lot barely 100 feet from the terminal entrance. "We didn't even have to take the shuttle."

An increase in air travel has made it difficult to find a vacant spot among the 7,800 parking spaces at the airport. On Wednesday, virtually every space was taken, forcing motorists to wait at the parking gates until another driver left. As of late afternoon yesterday, only 300 spaces were vacant.

"It changes by the hour," said Tara Hamilton, a spokeswoman for the airport, which has set up a 24-hour hotline (703-417-PARK) to provide updated parking information.

Airport officials anticipate periodic parking shortages through the summer, something they started noticing last year. Following a dip in air travel after the attacks of Sept. 11, 2001, passenger levels now surpass pre-9/11 levels.

"The kids are out of schools, families are traveling, everybody's having fun, and, hopefully, they'll find a parking spot," said Mike McElwee, an airport operations duty manager.

Some travelers have honed their parking routines. Elizabeth Fuscaldo, a consultant who works in the District and flies home to New York City every Thursday, usually shadows a shuttle bus until a passenger gets off, then grabs the driver's spot.

But others have spent so much time circling the lots that they have missed their flights.

Gary Washburn of Laurel planned to catch a morning flight to Atlanta yesterday. But he said he lost 15 minutes driving around a garage before he could find a place to leave his car. But it was too late: He missed his plane.

"I've never seen it this bad," said Washburn, who flies out of the airport once or twice a month.

Vouchers helped Gwen Windham and Michael Griswold of Baltimore park at Reagan National.