IT IS EASY to understand why officials of Pan American World Airways are outraged at President Carter for his decision giving Braniff Airways the nonstop route between Texas and London. Pan Am needs the business and thought it was in the bag after the recommendations of the Civil Aeronautics Board went to the White House. But the President turned that particular recommendation around, and Pan Am's chairman is charging that political considerations are behind the reversal.

We don't know what politics had to do with the President's decision. We do know that it shouldn't have had anything to do with it. And we do find the explanation form the White House for the decsioon sowewhat unconvincing. It does not successfully refute the finding of the CAB's majority, which included Chairman Alfred E. Kahn, the President's own appointee, that Pan Am would provide better services to travelers and shippers. The President's desire to strenghten regional airlines - the explaination provided by the White House - should not automatically take preference over service.

In one sense, the decision may strenghten Pan Am in the long run at the expense of those regional airlines. It had been seeking domestic routes for longer than anyone cares to remember. When airlines like Braniff, National and Delta become transatlantic carriers in competition with Pan Am and TWA, the rationale that has kept Pan Am out of the domestic market slips away.

May be that, or something like it, is what the President had in mind. He is eager to increase domestic airline competition airline competition. But he had not previously made it clear he intended to apply the same policy internalionally. There are aboard enough airlines already for vigouous competition - if only governments would eliminate price-fixing, flight, limitaions and limited landing rights.