New York Air will introduce hourly shuttle service between National and Newark International airports beginning June 30, the airline announced yesterday.

The airline also will commence hourly service between Newark and Boston's Logan International Airport on the same day. The increased number of flights from Newark is expected to present a substantial challenge to People Express at its home base.

With the new service, Texas Air Corp. -- which owns New York Air -- appears to have found a legal way to eliminate any barriers to its acquisition of Eastern Air Lines without having to halt service in the lucrative East Coast corridor.

Last week, New York Air sold takeoff and landing rights -- or slots -- at National and La Guardia airports to Pan American World Airways for $65 million. That removed the major obstacle to the proposed merger, because Pan Am will replace New York Air as competition for Eastern's hourly flights between New York La Guardia and both National and Logan airports.

"The world has changed dramatically in the past few years, and Newark is changing as fast as any place," said New York Air President Douglas C. Birdsall. "Capacity has been going up steadily. Obviously, we are pleased to remain in the market."

In the past three years, traffic between National and Newark grew more than 26 percent.

The decision to begin shuttle service to Newark was based, at least in part, on New York Air's loss of several valuable slots at La Guardia in a lottery held earlier this year by the Federal Aviation Administration. The lottery was an attempt to give new airlines a chance to compete at crowded airports that cannot accommodate increased air traffic.

The shuttle will run on the hour between Newark and Washington and on the half hour between Newark and Boston. Prices will be unchanged on those routes: During peak travel hours, tickets will cost $79 between Newark and Washington and $69 between Newark and Boston. Off-peak travel will cost $49 on all the routes.

"This shows how deep the interest is in keeping that shuttle traffic," said George James, president of Airline Economics Inc. "It also suggests that the image of Newark as a subsidiary airport has changed or is changing."

New York Air's sudden introduction of shuttle service also is expected to deal a competitive blow to Pan Am, which has no experience and fewer facilities for that particular type of commuting service.

Because People Express has dominated the flight schedule at Newark, it has been viewed as a no-frills airport, and business travelers often have avoided it and used La Guardia instead. But during the rush hour, when roads from La Guardia to Manhattan can become clogged, it often takes less time to get into Manhattan from Newark.

New York Air has said that planes freed when it sold its shuttle service slots at La Guardia last week would be used in the Northeast, mostly to serve its hub at Washington Dulles International Airport and at Newark.

Although Birdsall would not reveal his exact plans for growth at those two airports, he repeated his commitment to Dulles yesterday.

Birdsall said that, by the end of the year, he expects to have at least 70 departures a day -- up from 53 today -- in operation at Dulles.