New York Air will be forced to reduce by a third its low-fare service between Washington and New York and to eliminate completely its Washington services to Boston and Newark if the Department of Transportation implements its proposed National Airport policy, the president of the airline said yesterday.

"And there can be no doubt that with elimination of New York Air's effective competition, fares will return rapidly to their prior levels, causing the loss of millions of dollars in consumer savings," NYA President Neal Meechan warned. His remarks came during the first of two days of hearings on the proposed policy at Federal Aviation Administration Headquarters here.

Meehan estimated that New York Air's reduced fares have saved its passengers alone almost $12 million, compared with the fares they would have had to pay before NYA entered the routes. Meehan said his estimate did not include the additional millions saved by consumers flying with his airline's competitors, who reduced their fares as a direct response to New York Air. He said NYA carried 132,000 passengers in June, up from 37,000 in January, the airline's first full month of operation.

The DOT policy is designed to reduce noise and congestion at National while promoting increased use of the more distant Dulles International Airport. The policy would reduce the number of flightly permitted the commercial airlines at National; bar jet flights there before 7 a.m. or after 10 p.m.; extend to 1,000 miles the so-called perimeter rule that limits nonstop flights to within 650 miles of National (except for seven cities that are already exempted from the limit); limit to 16 million the number of passengers who could use National annually; and improve ground transportation to Dulles through some form of subsidized bus transportation and the accelerated construction of a 2 1/2-mile road extending the Dulles Access Road to I-66.

In his testimony, Meehan charged that DOT's plan "blatantly discriminates" in favor of Eastern Airlines' Air-Shuttle, New York Air's major competitor, by continuing to allow it to run "extra sections" of flights, often 15 a day, without regard to its allocation of slots -- the industry term for takeoffs and landings. At the same time, the new policy would eliminate a provision of the airport operating rule that has allowed New York Air and four other airlines to operate flights in excess of their slot allocations. New York Air now has 21 slots a day, but has a total of 48 takeoffs and landings a day under the provision.