New York Air announced yesterday that it will offer passengers a special $29 standby fare on its regular $49 flights between Washington and New York during January.

The airline's decision to begin the promotional fare is in large part an attempt to stem the frustration of prospective customers who can't get through to the airline on the telephone.

"As a result of overwhelming public response, our phones are busy all day long," NYA president Neal Meehan said yesterday. "So, beginning Thursday, just come to our ticket counters . . . and we'll sell you the next available seat for just $29."

New York Air, which started service on Dec. 19, has a two-tier reserved-seat pricing system: The regular fare on eight of its 10 weekday flights is $49, compared with the regular Eastern Airlines Air-Shuttle fare of $59; the fare on two of New York Air's weekday flights and all of its weekend flights is $29.

During January, NYA will still sell $49 reserved-seat tickets for its regular flights for those who passengers who want to have a reservation and don't want the insecurity of not knowing for sure that they can get on a particular flight.

"We're saying to the others, 'We know you can't get through. We're working on our phone problem, but we have plenty of seats available and here's your incentive to go to the airport and stand-by,'" one NYA official said yesterday. (So far, New York Air has operated about half-full, with more seats on the $29 flights sold than on the regular-fare flights.)

The airline said standby passengers should check in at NYA's ticket counter at National Airport or New York's LaGuardia no less than 45 minutes before scheduled departure. At that point, the $29 tickets will be sold and a standby number issued.