Late afternoon clouds hover behind the Dulles International Airport. (John McDonnell/The Washington Post)

Dulles International Airport has seen a tough few years. Fewer passengers are flying into and out of the airport’s iconic terminal. Less cargo is moving across its tarmac. And with the global economy still sputtering, there’s no telling when the airport’s fortunes will turn around.

A solution, some Virginia officials say, is the long-debated Bi-County Parkway, a proposed road between Prince William and Loudoun counties that could serve as a new conduit for people and cargo passing through Dulles. Proponents say it would spur business development by offering a vital north-south link to the airport, giving businesses easy access to an international gateway.

With thousand of acres of undeveloped land and a Metrorail connection that the Metropolitan Washington Airports Authority aims to open in 2018, authority officials hope to build new facilities — perhaps offices and another hotel — on airport property to generate additional revenue. On the land around the airport’s runways, MWAA officials say new buildings to house cargo, including units that could store flowers, pharmaceuticals and other perishables, could boost the airport’s bottom line. They point to a soon-to-be built United Airlines maintenance hangar as an example of the airport’s potential to bring in more jobs and tax revenue.

“On the East Coast, there’s one airport that has the potential to grow, and that’s Dulles,” said John E. “Jack” Potter, the MWAA’s president and chief executive.

Supporters of the Bi-County Parkway argue that is why the road is needed. Opponents, however, contend that the road will not help Dulles as much as some supporters claim because the passenger and shipping volumes do not justify it.

Proposed bi-county parkway map with cargo and passanger volume charts.

The issue has thrust Dulles, which celebrated its 50th anniversary last year, into the latest round of a long-running debate over where and how Northern Virginia should grow. A groundswell of opposition has slowed the parkway’s momentum in recent months and highlighted a host of concerns, among them the prospect of more sprawl. But the road remains part of the state’s master transportation plan, and officials indicated last month that they are moving forward.

In an interview, Potter said the road link could help, but not on its own. “To me, the movement of people north and south, the movement of trucks north and south, helps all businesses in the area, including the airport,” Potter said. “But can we say that if the road is built, cargo will grow? No.”

Dulles has not been waiting to see what happens with the road before tackling the airport’s challenges.

To try to improve the traveling experience, the airport has added a first-in-the-nation system that provides real-time information on security line waits.

The airport is also trying to move beyond its core aviation focus. The MWAA negotiated changes last year in its Dulles lease with the federal government that could allow for a broader array of commercial activities on airport-controlled property.

As much as Dulles is struggling, its smaller sibling, Reagan National Airport, is booming, thanks in part to new legislation that has allowed more of the long-distance flights that were long dominated by Dulles.

Last year, Reagan had a record year with 19.7 million passengers passing through its gates, nearly a 5 percent increase over 2011 levels. At Dulles, the number of passengers moving through the airport decreased almost 3 percent from the previous year to 22.6 million. The amount of freight moving through the airport has also dropped. In the six-year period between 2007 and 2012 the amount of cargo moving through Dulles dropped by 90,652 metric tons — a decrease of 25.2 percent.

The cargo struggles have provided an opening for proponents of the Bi-County Parkway, who say the airport needs more road access.

Tony Howard, president and chief executive of the Loudoun County Chamber of Commerce, is one of the road’s most vocal champions. “It will benefit the airport and also the many businesses around the airport. It will steer commercial growth in areas around Dulles.”

Population growth has slowed in Prince William and Loudoun, but people are still moving to those communities, and supporters of the project say that it is better to build the parkway before local roads are overwhelmed.

Leo J. Schefer, president of the Washington Airports Task Force, a nonprofit group of business and community leaders that advocates for the airports, likens the need for the Bi-County Parkway to the early days of the Dulles Toll Road, when there was no roadway connecting it to Interstate 66. Building that three-mile connector made it easier for people to get to the airport and may have ultimately helped increase passenger traffic, he said. He envisions a similar scenario for the parkway.

“As companies come to this region, they come by and large because of federal government,” Schefer said. “But where they locate is a product of access to an international gateway. That access would be greatly enhanced if Prince William County can get a [faster] connection to Dulles.”

Del. Timothy D. Hugo, a Republican who represents parts of Prince William and Fairfax County, said that even if the road could help Dulles, it could hardly be considered essential in a region wrestling with so many transportation challenges.

“I think it’s a misallocation of resources,” said Hugo, who has taken a leading role in opposing the parkway.

In May, Rep. Frank R. Wolf (R-Va.) chided proponents of the project, saying they should not try to bolster their case by claiming that the road would increase cargo at Dulles.

MWAA officials have tried to stay above the fray, but the discussions come at a time when airport officials are trying to position Dulles as an international gateway for passengers and cargo — one that could compete with New York’s John F. Kennedy International Airport and ­Hartsfield-Jackson Atlanta International Airport.

Despite the phenomenal growth at National, MWAA officials know that their future — and the bulk of their future revenue — will come from Dulles, which faces a host of challenges.

Dulles has no all-cargo airline, despite having tried for years to lure one. Instead, most of the cargo shipped into and out of Dulles — electronics, computer components and pharmaceuticals are the most common — travels in the belly of passenger jets.

“If Dulles wanted to compete with areas like [Memphis and Louisville], they’re going to have a [tough] time,” said Steve Alterman, president of the Cargo Airline Association. “If they want to get more freight, they’ll have to create it, not steal from somewhere else.”

Alterman said a road like the Bi-County Parkway could help.

“If building such a road leads to other business development around the road, that could make a difference,” he said. “The development of Dulles as a cargo airport really depends on the ability to attract businesses that ship things.”

Alterman said the MWAA could also raise its cargo capacity by capitalizing on its growing share of the international passenger market. In March, Etihad Airways began daily service from Dulles to Abu Dhabi, United Arab Emirates, and last month, Brussels Airlines began direct service.

Brandon Fried, executive director of the Airforwarders Association, said that with 3,000 acres, Dulles has potential but also has a long way to go.

“Is Dulles going to become a player?” he said. “Maybe in the long term things will change, but while Dulles has a lot of destinations, it’s no JFK.”