WASHINGTON, 1 June — Across America, new airport security measures that call for passengers to arrive early to pass through stricter security checkpoints have given a huge boost air terminal restaurants and shops. Retailers at US airports are experiencing a sales boom in spite of a nationwide decline in airline passengers, down 12.9 percent from a year ago.

At Ronald Reagan Washington National Airport, where the number of passengers has dropped about 26 percent from a year earlier to 1.1 million in March, retail sales are up 9.2 percent in April compared with a year earlier.

The increased food and retail sales run opposite to the trend in passenger numbers at Washington Dulles International Airport, which are down 8.7 percent compared with a year earlier. About 1.4 million passengers used Dulles in March, the last month figures were reported.

After last September’s terrorist attacks, Reagan Airport, which is located adjacent to the Pentagon and just across the Potomac River from the White House, was closed for 23 days and reopened in phases during the next seven months.

The number of passengers nationwide in the second half of September dropped by about 50 percent while airlines racked up multibillion-dollar losses. Passengers have returned gradually but still represent only a little more than 87 percent of their numbers before Sept. 11.

Airport retail and food sales were sluggish for the first six months after the attacks both locally and nationally. Sales rebounded faster than the number of passengers.

Today, new airline security regulations will soon require that all baggage be searched for bombs or weapons. While most in the airline industry worry about longer passenger delays, the possibility of larger throngs of waiting fliers warms the hearts of airport retailers.