Hard times have come to Dulles International Airport.

Eastern Airlines, one of those big names every airport wants in its lobby, is pulling out its last four flights in September because "we just haven't made a profit at Dulles," according to Eastern vice president Morton Ehrlich.

Delta, Ozark and Piedmont have already left. Republic is cutting back service, including three daily nonstops to New York's La Guardia that were averaging only 21 passengers each. Every month this year, passenger traffic at Dulles has been down at least 20 percent from the same month a year ago.

"We have never seen anything like this at Dulles," said James A. Wilding, director of Metropolitan Washington Airports, which is the Federal Aviation Administration office responsible for running both Dulles and Washington National airports.

The problem has come up suddenly and has caught Dulles in the midst of a $9 million expansion. It has come, coincidentally, as the FAA and its parent Department of Transportation are debating the future of both airports. A formal federal policy for Washington's two airports is to be announced this week. It could make or break Dulles at a time when help has never been more needed.

In the first four months of this year, the number of passengers using Maryland-owned Baltimore-Washington International Airport increased a modest 1.7 percent over the same four months a year earlier. National Airport had an even more modest 1.3 percent increase. At Dulles, the number dropped 21.9 percent.

There is no single reason for Dulles' declining fortunes, according to airline executives and other experts interviewed. Instead, there are seven little reasons and one big one.

The big one is National Airport, which remains first in the hearts and minds of airline executives who want to serve Washington. Because of its convenient location 10 minutes from the Capitol, a flight at National is preferable to one at Dulles.

"We moved our Washington -- JFK Kennedy Airport in New York flight from Dulles to National, and it's full every night," said Trans World Airlines' John Corris.

Eastern Airlines found it was selling as little as 48 percent of its seats on flights from Dulles at a time when airline economics puts the break-even point at 68 percent. The break-even point is almost achievable at National.

The seven little reasons:

Baltimore-Washington International (BWI) has completed a five-year, $70 million reconstruction program and has been aggressively advertising its new facilities to Washington residents and the airlines. Delta, Ozark and Piedmont Airlines have moved all flights from Dulles to either BWI or Washington National. Eastern will follow.

BWI has attracted two cut-rate airlines, World and Texas International, which sell cheaper tickets to the West Coast and Texas than the Big Three at Dulles -- United, American and TWA.

Dulles has almost no short-haul destinations, so once a transcontinental passenger gets there, there is nowhere else to go. Conversely, there are no small cities, such as Norfolk or Richmond, feeding the transcontinental flights to Dulles.

Dulles is losing a substantial number of international flights to expanded international operations at the Atlanta and Miami airports. Passengers from the Southeast, who used to fly to Dulles to catch a plane for London, now fly to Atlanta or Miami.

The enormous jump in jet fuel costs has forced the airlines to cut use of older, inefficient jetliners such as Boeing 707s and McDonnell Douglas DC8s, which for years were staples of the Dulles trade. Most long-haul flights at Dulles are now made in more efficient jumbo jets, but fewer flights are made. In June, for example, there were 1,643 fewer flights than a year earlier.

Unlike other U.S. airports, Dulles requires passengers to ride from the terminal to the airplane, then charges the airlines $54.07 for each one-way trip by a mobile lounge. Some airlines don't like the mobile lounges, the costs involved and the fact that their schedules have to list mobile lounge departure time, not airplane departure time.

Bus service from downtown Washington to Dulles has been dreadful, according to several airlines and many passengers. The FAA agrees this has been a problem, but says it is improving. Meanwhile, the bus from downtown Washington to BWI has established a reputation for reliability and punctuality. BWI subsidizes its bus operator; the FAA does not.

These are not great times for anyone in the airline (or airport) business. The record traffic gains that airlines were enjoying a year ago as they began to experiment with new freedom from federal regulation to add and subtract destinations have disappeared in fare increases forced by higher fuel prices.

The cost of airline tickets has jumped about 40 percent in the last year and both business and pleasure customers have reacted by cutting their travel budgets.

Airline travel was down about 3 percent for the first six months of this year and "July is going to be worse," according to one industry insider who has seen the early statistics. Those facts have hurt all airports, but they seem to have hurt Dulles more.

Despite all the jokes about it being the airport out in nowhere, the fact is that Dulles has experienced steady growth over the past decade. It weathered the airline recession of 1974 and 1975 with at least as much grace as National and BWI. Between 1971 and 1979, Dulles experienced a 69 percent increase in passenger boardings versus 42 percent at National and 20 percent at BWI.

People like Dulles airport. The Airline Passengers Association, whose members are high-frequency business travelers, rate Dulles fourth in the nation in response to the question "Which airport provides the best facilities?"

Continental Airlines picked Dulles over BWIwhen it pushed east in January 1979 and now runs two nonstops daily to Houston and Denver.

"In fact our load factors [percent of seats sold] have been better this year than last year," said Continental's Harvey Wexler. "We have every intention of staying at Dulles."

So, apparently, do United, American and TWA, although all have trimmed transcontinental service, especially with 707s and DC8s.

The common perception from these facts is that BWI is beating Dulles in a two-way struggle for the traffic that doesn't use Washington National.

However, if all passengers boarding at all three airports are considered to be one potential market, then the loss at Dulles mostly has been a gain for National.

This is just another chapter in what National has done to Dulles over the years.

When Dulles was opened in 1962, it was supposed to be the new jetport for Washington because the first jets were too big to land at National. But smaller two- and three-engine jets were let into National four years later, so Dulles kept only the transcontinental and international traffic.

Although quotas were imposed on flights at National to ameliorate the noise problem that remains today, that did not stop National's growth. Airplane manufacturers found ways to stretch the Boeing 727s and McDonnell Douglas DC9s so more people could fly in them. Another blow to Dulles.

If two- and three-engine jumbo jets are permitted at National -- one of the elements expected in the Federal Aviation Administration's upcoming airport policy -- it will be another blow, unless a ceiling is placed on the number of passengers permitted to use the airport. If the ceiling were low enough, it would force flights to Dulles and BWI regardless of the size of the planes using National.

The FAA, as Dulles' owner, would seem to have an economic incentive to help Dulles. But in a neat accounting trick, Dulles and National are carried by the federal government as one operation.

If the bottom lines were sorted out, National made $10 million for the U.S. treasury last year and Dulles lost $1.5 million. Nonetheless, Dulles' performance has improved over the years and "we thought we were inching toward the black" for the first time, the FAA's Wilding said.

Another economic issue is also at work. If too much traffic is shifted from National to Dulles, a tremendous investment that has already taken place in the Crystal City area adjacent to National Airport could be affected.

According to Arlington County officials, there are 1,936 hotel rooms in Crystal City, with an additional 615 under construction. Furthermore, if development in nearby Pentagon City is counted, more than 3,000 additional hotel rooms are planned.

'No one has specifically said they would stop their developments if the National Airport picture changes dramatically," said Arlington County planner Tom Parker, "but I'm sure they're thinking it."

There are only two hotels at Dulles, with a total of 344 rooms. Phil Wilner, innkeeper at the Dulles Holiday Inn, said things there aren't too great. "We are down," he said. "We're finding it hard to attract groups or seminars here because you can't get here. Why should you take a plane to National, then bus out here?" He said his hotel-to-airport shuttle service is "off 15 to 25 percent" from a year ago.

The $9 million expansion was undertaken to ease luggage-handling and passenger congestion that Dulles suffers between 5 and 7 p.m. daily, when almost half of its passengers use the airport. That is the prime time for both West Coast and European flights.

Great care was taken by the FAA in planning the expansion to make sure the original outlines of Eero Sarrinen's architectural masterpiece -- the Dulles terminal -- were preserved.

For Dulles eventually to prosper, officials agreed, it must be easier for people to get to the airport than it is now, and constraints must be placed on National.

The Virginia Department of Aviation has just opened an office at Dulles to promote the airport and the FAA is about advertise a new contract for bus service to the airport.

Interstate Highway 66 inside the Beltway is nearing completion. The Dulles Access Road will be extended from Tysons Corner to I-66, probably by the end of 1984. That should dramatically improve the ease with which a driver can get from downtown Washington to the airport.

Metro subway extension is often discussed, but nothing is in the works.

A lid on passenger growth at National Airport has been proposed by three consecutive secretaries of transportation but never implemented, largely because of congressional pressure.