Eastern Airlines will reinstate service at Dulles International Airport on June 1 with a daily nonstop round trip to Atlanta.

The reintroduction of Dulles service by Eastern, which hasn't had any flights there since September, is part of an ambitious expansion program under which Eastern will begin new service on 10 international and five domestic routes and will add numerous flights to existing routes between April 26 and June 1.

Eastern's expansion plan is just one of many in the industry as airlines use the opportunities presented by airline deregulation to restructure their route systems in time for the peak summer travel season.

For instance, on June 11, American Airlines plans to begin service from Dallas-Fort Worth to 11 cities it doesn't serve now. It also will be starting seven new routes between cities it already serves.

Due in large part to the entry of New York Air on the Washington-to-New York route with low fares and partly because of its plans to increase service outside of the Northeast, American dropped its last three roundtrip flights between Washington and New York last week, American officials said.

Despite a considerable amount of route movement, Dulles International doesn't appear to be slated for any increase in domestic service -- at least not right now -- despite incentives offered the airlines by the Department of Transportation. In November, then-Dot Secretary Neil Goldschmidt sought to make Dulles more attractive to the airlines by waiving landing fees and mobile lounge charges.

Besides Eastern's new service intentions, the only other airline to respond was Air Florida, which began service between Dulles and Miami in December. Dexter P. Davis, airport manager at Dulles, said yesterday he knew of no other airline with plans to move services to Dulles. "I wish the picture was more optimistic," he said.

In another development, New York Air announced at the weekend that it was dropping its fare between Washington and Boston on Saturday nonstop flights to $39 each way to encourage Saturday travel. Its regular Washington-to-Boston fare is $69, compared with a regular coach fare in the market of $108. Other airlines flying the route have met New York Air's price, at least for some of their seats.

In another airline development that could affect Washington-area travelers, Pan American World Airways resumed daily nonstop service last week between New York and Paris, with connecting service from Washington's National Airport.