Washington Dulles International Airport is losing passengers in droves as travelers flock to Baltimore/Washington International Thurgood Marshall and Ronald Reagan Washington National airports to catch domestic flights.

The international airport in Virginia had 134,000 fewer passengers in July compared with the same period last year -- a 6 percent decline, according to the most recent data -- even as business at the region's two other airports hit highs.

The Metropolitan Washington Airports Authority, which oversees the two Virginia airports, attributed the drop in Dulles traffic to the addition of low-cost flight options and long-distance flights at Reagan. That competition, coupled with an overall decline in domestic air travel nationally, is putting pressure on Dulles, the authority said.

"This trend is consistent with other airports across the country. In response to economic conditions, airlines have reduced or constrained domestic seats in favor of international service," said authority spokesman Rob Yingling. "We expect Dulles domestic passenger numbers to bounce back in the future as the airlines shift more capacity there to accommodate demand."

International travel at Dulles has grown slightly -- 0.9 percent -- over last year, though it grew by 17 percent at BWI over the same period.

The shift of domestic passengers to Reagan National is making things more expensive at Dulles, officials said.

The additional flights at Reagan "have shifted similar service away from Dulles International, escalating that airport's costs and, therefore, expenses to airlines," authority CEO Jack Potter wrote recently to federal authorities.

BWI charged airlines $9.29 per passenger over the last year, while Reagan charged $12.74 and Dulles charged $26.03. Yingling said Dulles' costs are higher because of the significant costs of recent improvements, including construction of a fourth runway and new parking garages.

Those costs translate into higher ticket prices for passengers using Dulles.

The average round-trip domestic fare at Dulles was $485 in the first quarter of 2012 -- the fifth-highest in the nation, federal statistics show. Fares at Reagan averaged $390, the 39th-highest, and $330 at BWI, the 79th-highest.

BWI Executive Director Paul Wiedefeld attributed his airport's growth to a strong local economy, a variety of destinations, low costs and easy access.

"We focus on making sure we have the airlines that respond to what the market wants," he said.