Washington-area travelers probably will be able to catch an increasing number of flights to more places from Washington's two outlying international airports because of passage of the Airline Deregulation Act and the Carter administration's pro-competition international aviation policy.

Because Washington National Airport is virtually closed to newcomers - not even airlines already serving there can add flights without subtracting others - the new law's provisions facilitating formation of new airlines and expanding of existing airlines to new routes virtually gradutates increasing services at Baltimore-Washington International Airport and Dulles International Airport.

Barely a month after President Carter's signed the deregulation bill, it is beginning to have an impact. Next month, for instance, Air Florida, a successful intrastate airline begins service from Dulles to Ft. Lauderdale and, pending CAB approval, Miami. It will be the only Florida-bound service from Dulles. Also because of the bill, BWI will get additional air service to Tampa, Fla., when Allegheny Airlines starts up its new route.

Although the new law is designed to increase competition in the airline business in a number of ways, most important - and the reason why BWI and Dulles are sure to be affected - are provisions which encourage new firms to enter the industry and existing carriers to expand into new markets.

A provision allowing airlines to pick up the unused route authority of other airlines already has generated the new Florida services, and other route awards through this vehicle are expected.

New routes from the Washington area also may result from the "automatic entry" provision allowing each airline to pick one new route a year without going through Civil Aeronautics Board hearings.

Even getting routes in the traditional way - through the application process - will be easier, cheaper and quicker because the new law removes many of regulatory and procedural obstacles and sets strict time limits.

It is these provisions allowing freer entry that are bound to affect Dulles and BWI. Although National is still the first choice airport of area residents because of its convenience and connections, any would-be airline or incumbent airline wanting to add service here is forced to do it at one of the two outlying airports.

Washington National is operating under what the Federal Aviation Administration calls a high-density rule, and is limited to 60 takeoffs and landings an hour. All those "slots" are taken by the airlines currently serving National: Ten certificated airlines serving National share 40 of the flights, the private owners of planes have 12 an hour, and the commuter airlines have 8.

Even if the slot arrangements were changed - there is some attention being paid to the question of whether they should be altered - there are additional obstacles for expanded operations at National. Its operating hours (7 a.m. to 10 p.m.) are relatively short, it is limited to narrow-bodied planes - although that too is under study - and carriers cannot, at least right now, fly nonstop to any city outside a 650-mile perimeter (unless it is to one of seven cities being served by propeller planes from National before jets came in in 1966).

"The natural spillover of demand will have to be fulfilled at Dulles or EWI," Philip J. Bakers, CAB's general counsel notes.

Even before the deregulation bill was signed, the CAB's pro-competition policies, combined with National's constraints, had spawned the beginning of additional service plans at the two out-lying airports. For instance, Texas International Airlines and Continental Airlines both were given new authority to Houston from here and were forced to look to the outlying airports.Continental already has announced plans to fly from Dulles, and TXI still isdeciding but is likely to use BWI.

The pro-competition policy the Carter administration has been pursuing in international aviation also is expected to affect the area's two secondary airports. The administration has been trying to get other governments to agree that the U.S. can designate as many airlines as it wants to fly between the U.S. and their countries and also has been allowing those countries to add to their U.S. points in exchange for other pro-competition provisions.

As a result of the agreement with Belgium, Sabena, the Belgian Airlines, is able to pick two new U.S. cities immediately and is understood to be interested in Washington as one of them.

Any increased international traffic - which necessarily goes to BWI or Dulles - also could increase domestic connecting service at those airports. If the larger domestic airlines do not add feeder service smaller ones - such as the commuter airlines - may tailor their systems to some extent to serve passenger on international flights, CAB officials believe. Commuters are now able to fly planes with up to 55 seats compared to 30 before.

All of this can have a snowball effect the airline and airport experts believe. "Service feeds upon itself," says Michael E. Lewine, director of the CAB's Bureau of Pricing and Domestic Aviation. The more airlines servicing an airport, the more valuable and desirable it becomes for others because of the connecting services, the traffic flow.

"National is an important connecting complex right now, but either BWI or Dulles could become a more genuine alternative," he says.

In this new environment BWI already has shown itself to be a very vigorous competitor for new air services and appears to be outstripping Dulles so far in attracting new airlines. It has one distinct advantages a state-funded marketing budget of more than $300,000 a year and several full-time employes who do nothing but seek increased air services at BWI.

"We have an incredibly elaborate marketing program," said Kari B. Sattler, BWTs administrator. For instance, using economic analyses, airport officials decide what cities should be served from BWI and go out looking for an airlines to serve them. They first try to get an in-house airline to expand its network to include a city the airport officials think would prove lucrative. If they are not successful, the airport's personnel go out to find a new airline to come in and serve the additional city. Presentations are tailored to the specific airline, laying out the potential passengers and profits.

BWI officials also use as a selling point that BWTs location between Washington and Baltimore allows it to draw passengers from both. "BWI is really coming into its own now," Sattler said. "The airlines are recognizing us as a Washington airport."

The vigorous marketing program clearly has paid off. In the last couple of months, a number of airlines have started up service from BWI, including North Central Airlines, Icelandic Airlines and Caribbean Airways. Applications from other carriers are pending.

Dulles is getting new service too - it grew by more than 10 percent over the last year - but it is not service that was sought in a marketing sense. Unlike BWI, which is owned by the State of Maryland, Dulles and National are owned and operated by the federal government, which doesn't believe in spending the taxpayers' money to promote Dulles. "I don't think it's an appropriate federal function," says James T. Murphy, director of the Metropolitan Washington Airport Service under the Federal Aviation Administration.

"We're not trying to force-feed Dulles; our major concern is to try to come up with a mechanism to rationally control growth at National," he says.

Even without allowing more flights into the airport, National's passenger traffic has been growing substantially - 900,000 over the last year - in part because the airlines are using more of the larger, narrow-bodied planes. Growth is expected to continue somewhat, but the FAA hopes that it will slow so that National will serve a maximum of 16 million passengers a year by 1965 and 18 million by 1990.

National currently accounts for 68 percent of the area's air passenger traffic, with more than 14 million persons a year flying in and out for an average of about 40,000 a day, BWI and Dulles split the rest of the traffic almost evenly with between 3 and 3.5 million passengers a year.

The FAA's Murphy said he's not sure what the total capacity of National is. "Like a family for Thanksgiving, there always seems to be room for more." Although there are certain constraints - public parking ticket counters, baggage handling and the like - nevertheless it seems that "If people want to travel they somehow manage to do it, even if the amenities are lessened and it's more crowded," he noted.

Facilities at both BWI and Dulles are being revamped to make the airports better equipped for whatever the future holds. BWTs renovation of terminal facilities is already 80 percent completed and allows the airport in its current shape to handle up to 115 million passengers a year compared with the 3.5 million it now serves. With some modest capital improvements, 18 to 20 million could be accommodated, Sattler says.

Renovation at Dulles is just starting. The 16-year-old airport is in the midst of a $7 million reconstruction program to enlarge passenger and baggage-handling facilities, but gate capacity won't be affected. Right now, 12 of the airport's 24 gates are closed (not more than 17 ever have been used at any one time and temporary facilities are accommodating the usual passengers much more smoothly than anyone expected, according to Dulles Airport Manager Dexter P. Davis. Because the international flights in and out are bunched in the late afternoon and early evening, Dulles right now has a horrible "peaking" problem with more than 35 percent of each day's traffic moving through the airport between 4 and 7 p.m. Davis hopes that any increase in services to and from Dulles avoids this rush-hour period.

A substantial expansion of Dulles' facilities is not scheduled until 1985 although Davis is trying to improve airport facilities such as parking. (One day last week, the airport's 3,300-space parking lot overflowed, a problem expected to get worse as air services increase unless some changes are made.)

Of course, the airline deregulation bill could reduce some service from Washington if airlines find they would rather use the airplanes they have on other routes. But no one seriously expects demand for air service here to slacken. Washington is still a great tourist attraction and continues to grow as a business and cultural center, not to mention the above-average-income clientele for the airlines the Washington area itself provides. Barring any drastic change in the operating policies of National, the expected growth in air service will take place at BWI and Dulles.