IN CASE YOU missed it, we want to call your attention to the travel bargain of the year. For $99, Pan-American World Airways will fly you from Boston to Amsterdam, and for $50 it will bring you back. Of course, there are no "frills," you bring your own food and refreshments, you have to stand by and hope a seat is available on both flights, and the fares are good only until July 15. But the price for a round-trip to Europe is hard to beat. The current Boston-Amsterdam "economy" fare is $812, and the cheapest New York-London fare is 243.

The loss leader is a new concept for the airlines - this one was designed by Pan-Am to advertise a new route. The management, reflecting the old airline skepticism about the quick reaction time of passengers, didn't really believe the bargain would draw an immediate crowd. It did. The plane took off full, and 65 would-be passengers were left at the gate when the fares went into effect three days after they were announced.

That's just one of the dozens of bargains that are scattered around the airline world now. United Air Lines, for example, offers 11 different prices, ranging from $248 to $538, for round trips from Washington to Los Angeles. Eastern Air Lines will fly you to almost anywhere it goes for a little more than $300; it says you can visit Seattle, Los Angeles, Mexico City, Jamaica, Trinidad and Bermuda on one vacation - if you have the stomach for it. Pan-Am will fly you around the world for $999. And so on.

All these cut-rate fares are limited by much fine print. You usually cannot reserve a seat, which means you fly only if the flight is not fully booked. You may have to travel on certain days (or nights), put up your money long in advance, stay specified lengths of time and who knows what else. The fares are so complex that not even all of the ticket agents have mastered them. And that has made shopping for a ticket as difficult as shopping for a new car. No one source, other than, maybe, a good travel agent, will (or can) tell you about the bargains available on all the airlines.

This brave, new world of price-cutting is a product of the Civil Aeronautics Board's desire to introduce the airlines to price competition. The board is approving new rate schedules almost as quickly as they are filed, and it seems willing to let the airlines experiment with almost any kind of new deals they can design.

So far, at least, that policy has worked to help the airlines as well as the travelers. The number of people flying somewhere was up sharply this May from the same month a year ago. Some airlines are substantially increasing the number of flights between certain cities in the belief this travel boom will continue all summer. And a few airlines are swamped with telephone calls from those who want to explore the new travel possibilities.

If the boom does continue, the evidence will at last exist to support one of the key arguments for greater deregulation of the whole airline business. proponents of deregulation have long claimed that lower prices and real price competition would generate enough new passengers to increase total revenues significantly. If the validity of that argument is demonstrated in the next few months, at least some of this summer's air-travel bargains will become part of a regular summer sale.