The Civil Aeronautics Board yesterday tentatively awarded World Airways the authority to fly between Boston and London, effective June 1, at a fare about half that now being charged.

World's proposal, which won out over the applications of four other airlines would establish an unrestricted, reserved-seat fare that will apply to all seats on its flights, similar to the one-class service and fare World offers on its domestic flights.

In halving the fares currently being charged on the Boston-London route, World told the board it would charge $224 each way during the summer peak flying season and $174 each way during off-peak periods. Trans World Airlines, which now flies the route along with British Airways, is currently quoting $364 each way for an unrestricted normal coach seat during off-peak periods and $444 each way during the peak season.

The addition of another U.S. airline to the route was made possible under the terms of a recent amendment to the U.S.-United Kingdom bilateral air services agreement.

The board's tentative award to World, subject to a final order and President Carter's approval, is for temporary authority over the route, presumably through the end of the year. Although the board has instituted a proceeding to determine which airline should be awarded permanent authority over the route, it wanted to make sure a U.S. airline could operate this summer during the peak travel season.

At the same time World was announcing that it was lowering its fares, a trade group representing 26 airlines asked the CAB to lift its rules and gave airlines the flexibility to raise fares immediately by up to 50 percent on short flights and 30 percent on longer ones.

The petition was filed by the Air Transport Association in response to a CAB call for comments on proposals to give airlines more flexibility to alter fares both up and down without CAB interference.

The ATA, however, argued that it would be "impractical" and "contrary to the public interest" for the board to maintain current procedural dates that allow comments until May 12 before considering the proposals on their merits. They were put out for comment on Monday.