President Carter overruled the Ciivil Aeronautics Board yesterday and approved lowcost transatlantic air fares.

The President approved a $256 round-trip budget fare between New York and London, and advanced purchase excursion ("super-APEX") fares ranging from $290 to $440 for round-trip service between London and eight U.S. cities, including Washington.

The new "super-A P E X" roundtrip fare between Washington and London will be $323.

These are "winter rates," which will be followed on April 1 by slightly higher "summer rates."

Carter's action came the same day that the British based Laker Airways began its so-called "Skytrain" service between London and New York. The no frills, no reservations Laker service costs $237 round trip. The competitive threat that the Laker fare posed prompted U.S. airlines to seek the lower fares that the CAB rejected and which the President approved yesterday.

The "super-APEX" plan requires that tickets be purchased 45 days in advance and that travelers return to their homes 14 to 45 days after leaving. The new "super-APEX" fare will be $290 round trip between New York and London, and slightly more between London and the other U.S.cities where it is available. The old "super-APEX" fare between New York and London was $350 round trip.

Under the budget plan, a traveler must buy his ticket three weeks in advance and can specify only the week in which he wants to travel. Ten days before departure, the airline must imform the traveler of the exact date and flight number for his journey.

The CAB recently approved a $280 budget fare. However, expressing fear that lower fares for scheduled airlines would damage the charter airline business, the agency rejected the $256 budget fare sought by the airlines as well as the $290 super-APEX fare.

The President's action yesterday does not affect a CAB-approved $256 round trip standby fare between New York and London. Under the standby fare, which will now cost the same as the budget fare, travelers have no reservations and must await at the airport for seats to become available on flights.

In a letter to the CAB yesterday, Carter said, "I have decide to reject the board's order as inconsistent with this administration's foreign economic policy. I must emphasize that my international aviation policy carries with it a commitment to low-fare, competitive international air service for the benefit of American consumers."

According to White House officlas, the president also urged the CAB to remove fedeofficials, the President also urged the CAB to remove fedee Departments of State and Transportation will soon begin discussions with European government aviation authorities on removing such restrictions on charters and other low-fare transaltantic air service.

The fares approved yesterday are effective immediately although under the super-APEX plan travelers will not be able to leave for London for at least 45 days. They are considered winter rates and will be available until March 31.

In the meantime, according to White House officials, Transportation Secretary Brock Adams will study how well the new fares serve the public and how to make low-cost transatlantic air service more widely available.

Regular, tourist-class round-trip air fare between New York and London is $629 during the winter season. First-class, lusury service costs up to $1.312.

In addition to New York ($290) and Washington ($323), the other cities with super-APEX service and the new round-trip fares will be Boston ($285), Philadelphia ($313), Chicago ($353), Detroit ($336), Los Angeles ($440) and Mtami ($332).