BY FLEXING its muscles for one of the few times in the recent history of international aviation, the U.S. government apparently is succeeding in driving down the price of many trans-Atlantic air fares. As a result, trips to Europe this summer will be a bargain compared with prior years for those who have the time and inclination to meet the restrictions of low-cost fares. If you are among them, you can think the White House and the Civil Aeronautics Board for making good on the president's pledge to open up the airways.

The struggle began, of course, with Laker Airways' cheap New York-London fare. Other airlines were allowed to cut prices to meet the competition on that one route, but the British government did not want the lower fares to spread to other routes.When Braniff proposed using a similar low fare on its new Dallas-London run, the British said no. The CAB, which had approved the Braniff proposal, stood by its guns - a welcome depature from past performance - and recommended that the president retaliate by stopping British Caledonian Airways from flying between London and Houston. Mr. Carter postponed doing that for a few days, but as the word was passed that the White House was also considering repudiation of the British-American air treaty signed only last summer, the British position began to crumble. It collapsed with the announcement that the United States and the Netherlands have agreed to permit low fares and wide-open competition on flights between this country and Amsterdam. The pattern set in that agreement will probably now become standard, at least for a time, throughout most of Europe.

Washington has rarely been this aggressive in bringing its influence to bear on the pricing of international transportation. All too often, it has left the setting of fares largely in the hands of the airlines themselves and their international organization. In that forum, the American airlines are at a disadvantage because they are private companies and most of their competitors are not. By stepping into this situation so forcefully, the White House and the CAB have made it clear that they intend to push their ideas of competition and lower prices as vigorously in the international as the domestic field. That stance is not likely to win them any applause in foreign capitals where the goal has been to keep prices high and competition low. But it ought to win them considerable praise here at home.