Eastern Airlines will discontinue its half-price Youth Fare plan beginning April 28.

A new youth fare program will eliminate standby and allow people under 22 to make flight reservations for two-thirds of the regular price. Youth fare cards purchased before the change will be usable.

National and Braniff Airlines will change to the same two-thirds assured space plan at the time that Eastern does. Delta and Allegheny have offered this as their sole youth fare program for several years. Northeast has used the plan on its Boston-Philadelphia route since February 25 as a test of youth response to a possible total change in its youth fare program.

TWA, United, and American, the airlines that specialize in long-haul, nonstop flights, will not change their present half-fare plans.

The two-thirds fare will be effective at all times on the Eastern shuttle. Other Eastern flights will be open to youth fare passengers only from noon Monday to noon Friday, and noon Saturday to midnight Saturday until May 31 when the restrictions on travel between midnight Friday and noon Saturday urday will be lifted.

Buses Grumble

The change comes as a response to widespread dissatisfaction with the standby system as used by the shortrun airlines. Eighty per cent of the population of the United States lives within the Eastern route systems, and heavy congestion in standby lines left many students flight-less and caused chronic delays in departure times.

Complaints from the nation's bus lines have also forced airlines into a re-examination of their reduced fare policies. Trailways Bus Lines is currently seeking an injunction against Eastern for the severe losses the surface companies have suffered since the advent of youth fare.

Thomas E. Mullen, Manager of Special Merchandising Programs at Eastern, said yesterday that he does not expect the airlines still operating at half fare to pose a threat to the two-thirds programs.

He said that in a study made by Eastern of 300 students in the Eastern route area, students overwhelmingly favored the two-thirds assured space plan.

Military passengers will continue to fly half fare standby.