THE DESIRE of some airlines to escape from guaranteed ticket prices is understandable. They sell you a discount ticket in January for a trip that begins in June. In the interval, fuel costs go up and so do ticket prices. It would be nice, for the airlines, to collect the difference.

Western Airlines points out that this difference is costing it a pot of money. A 9.5 percent fare increase, which it was granted last September, for instance, has produced only a 4.5 percent to 5 percent increase in revenues. Many of its passengers, obviously, are paying less for their transportation than Western (and the Civil Aeronautics Board) thinks they should.

But that, it seems to us, is the way marketing works. If an airline agrees to fly you to the West Coast six months hence for $200, it should be held to its bargain. Tacking on a "fuel surcharge" (or whatever you want to call it) of, say, $19 not only can spoil a vacation but also can be regarded as reneging on a promise.

Most domestic airlines have been guaranteeing prices as a good business practice without any nudges from the CAB since discount fares became popular a couple of years ago. Now that some are having serious second thoughts, the CAB should write into its rules a requirement that the transportation must be delivered for the original price. A ticket is a ticket, and it ought to get you to the place you want to go at the price you agreed to pay.