Some discount air fares between New York and the West Coast will drop sharply next month as a result of a Civil Aeronautics Board action yesterday.

The agency said it would allow American Airlines to put into effect a new "Super-Saver" discount fare on flights between New York and Los Angeles and New York and San Francisco that will allow consumers to purchase a round-trip ticket for $227 to $268 round trip, depending on the day of the week.

The current New York-West Coast round-trip coach fare is $412; the fare, with advance-purchase and minimum stay requirements similar to those of the "Super-Saver," is $330.

Although they opposed American Airlines' proposal, arguing that the new fares would be uneconomic, both CAB-approved round-trip excursion United Air Lines and Trans World Airlines filed applications at the same time to meet American's fares if they were approved, so all three carriers will offer the "Super-Saver" cross-country fares.

The new fares require consumers to purchase the ticket at least 30 days prior to departure and stay between 7 and 45 days. The fare for travelers on Thursday, Wednesdays and Thursdays will be $227 round-trip; travelers on Mondays and Fridays will pay $247 round-trip; and Saturday and Sunday tickets will cost $268 round-trip. The round-trip cost for children -- all times --

The fares go into effect March 17 for travel on or after April 24. As with current excursion fares, not more than 35 per cent of any airplane's seats could be used for "Super-Saver" travelers.

Washington area travelers would save very little by flying to New York and then to the West Coast on the "Super-Saver," probably not enough for the extra trouble involved. Although the current round-trip coach fare between Washington and the West Coast is $392, the current excursion fare -- buy your ticket two weeks in advance and stay a minimum of seven days -- is $314. Even with the $227 mid-week round-trip "Super-Saver" ticket, the additional $76 Washington-New York round-trip ticket would boost the cost to $303, just $11-less expensive-than the current direct excursion flight.

The CAB didn't technically approve American's proposal. As it did recently when Texas International Airlines applied for permission to cut fares in half on certain of its flights, the board yesterday said it would allow the fares to go into effect for the year period proposed, but would begin an investigation to determine whether they are lawful and just under the Federal Aviation Act.

The board said yesterday it had "significant reservations as to the economic soundness of this fare for scheduled service" but added, "on the other hand, we are reluctant to deny the carrier an opportunity to implement what it considers to be a fully warranted pricing experiment."

The board noted that American's fare proposal was designed in part as a major competitive response to the Advance Booking Charter programs it authorized in the fall but which are just now being developed and promoted. Charter tour operators had urged the board to reject American's new fares on the grounds that they could doom the new type of air fare-only charters that impose fewer restrictions on both travelers and charter operators than previously-approved charters had.

Noting that typical prices for New York-Los Angeles ABCs range from $179 to $249 round-trip, the board added, "the fact remains that those travelers seeking the lowest air-trans portation cost will still find an ABC charter the best bargain."

Robert L. Crandall, American Airlines senior vice president for marketing said yesterday the board action was an indication "that the industry has the ability to provide low-cost air transportation under the existing regulatory system."

Noting that American's proposal came suspiciously close to the opening of Senate hearings next week on proposals to alter the air regulatory framework that has been in place since 1938, one industry critic asked, "where the hell have they been the last 39 years."