AUGUST is the month when much of Congress sets out to improve its understanding of the world -- a quest the public should applaud if only because it keeps Congress from doing worse things. Many senators and representatives will be speeded on their way in military planes. The Defense Department, however, has informed members of the House Energy and Commerce Committee that they will have to travel abroad by commercial carrier because it lacks the planes to accommodate them.

The committee has not formally objected to the rejection of its travel request. But some members, noting that the department had been encouraging about the request when it was first made, wonder whether the final rejection was influenced by factors other than equipment shortages. They point out that, in the interim, Chairman John Dingell held highly publicized hearings revealing abuses by General Dynamics and other contractors.

In response to press inquiries about the matter, the Defense Department replied that its policy is not to discuss congressional travel requests -- a policy that Congress surely endorses as a gen- eral matter. In fact, it's fair to say that Congress' usual unwillingness to deal with its own travel requirements in an up-front manner is ultimately to blame for the fact that the department has this much power over congressional travel plans. As things now stand, committees can decide to purchase commercial airfares for a given trip or they can request a military plane. Either way they are supposed to list the cost in quarterly reports printed in the Congressional Record (although not summarized in any readily accessible way). For some trips -- specifically when a sizable number of members are traveling to remote locations -- military planes may be the most economical choice. But the fact that military transport costs are buried in the big Pentagon budget -- rather than charged against committee budgets -- surely tempts committees to call for military planes when commercial fares would cost taxpayers less.

Another hidden price of this arrangement, of course, is that it gives the Pentagon final say about which congressmen have access to its special services. That's not a healthy situation. But the way to deal with it -- and to make sure the taxpayer isn't overcharged -- is not to castigate the Pentagon. Instead, Congress ought to have the courage to vote itself the travel funds it needs. Then members can decide whether it makes financial sense to go commercial or military and, if the latter, to order up a military transport on a first-come/first-served basis. There's no such thing as a free trip either.