Travel price cutting continued yesterday with Trans World Airlines proposing discount fares on seven routes including two in and out of Washington, Delta Airlines slashing its New York to Miami rates, and Greyhound undercutting Delta on the same run.

Delta said its no-frills "Aero-bus" service to Florida would cost $55 one way on Monday, Tuesday and Wednesday and $75 on other days.

The Greyhound bus fare is $75, but Greyhound president Harry J. Lesko promptly proposed a $49.95 one-way excursion ticked from on the New York to Miami route.

All the fares required the approval of federal regulatory agencies and include many restrictions.

TWA said its "Fuel Saver Fare" will offer 25 per cent off on coach tickets but only on Tuesdays and Wednesdays between Jan. 10 and Feb. 28. The fares would be offered from Washington to Los Angeles and San Francisco, from New York and Boston to Los Angeles and San Francisco and from Philadelphia to Los Angeles.

On those days on those flights in those months there are many empty seats, the airline said. One nonstop flight on each route will be eliminated and the cheaper fares offered on flights with stops.

TWA said no advance purchase of tickets or reservations would be necessary.

Delta said its plan would create a new kind of air service with no meals, no limit on the length of stay and no requirement for advance tickets or reservations.

For $55 or $73, Delta passengers would fly in stretched DC-8 jets with what the airline described as "high density seating."

National Airlines said it would match Delta's New York-Miami Fare, "No one has lower fares than National and no one will," a spokesman vowed.

Delta pointed out that its $55 fare undercuts Greyhound by $20 and is only 50 cents more than Amtrak's fare. The jet flight from New York to Miami takes 2 hours, 45 minutes, compared with 27 hours on the train and 31 hours on the bus.

Greyhound, however, said it "will not be underpriced" by the airlines and will seek an under $50 fare for one bus a day each way starting Dec. 15, the same day the Delta flights would begin.Delta's Acro-bus would offer four flights daily in each direction.

The air fare reductions require approval of the Civil Aeronautics Board; the bus fares have to be reviewed by the Interstate Commerce Commission.