Pan American World Airways yesterday announced new Washington-to-New York air service with initial fares as low as $30.

It was the second time in less than a week that a major airline has announced new low-fare service between New York and Washington to compete with the Eastern Airline shuttle.

Texas Air Corp., which owns Texas International Airlines, earlier this week announced the creation of a new airlines, New York Air, to compete with the shuttle with one-way fares as low as $29 during evenings and weekends. The new air service, which must be approved by the federal government, is scheduled to begin Dec. 14.

Pan Am said it would begin round-trip daily service between Washington's National Airport and Newark Airport on Oct. 26 with four flights in each direction. The airlines said oneway coach fares for the first 30 days of the new service would be $30 and first-class fares would be $50.

Eastern, which has a near-monopoly on the Washington-New York service, charges $60 for a one-way flight. The shuttle does not have a first-class section.

Unlike the shuttle, which guarantees a seat to everyone who shows up in time for a flight, both Pan Am and New York Air will require reservations.

Pan Am said its flights from Washington to Newark will depart at 7:30 a.m., 9:15 a.m., 12:30 p.m. and 5:20 p.m. Departures from Newark to Washington will be at 7:30 a.m., 10:45 a.m., 3:30 p.m. and 7:40 p.m.

Asked if the low fares were likely to be continued after the first 30 days of service, a Pan Am spokesman said yesterday "that remains to be seen."