When the no-reservation transatlantic airfares begin in September, the price of a vacation in Europe will compare favorably with such popular domestic excursion as driving downtown and putting the car in a parking lot. But at the same time, the possibility of even cheaper vacations for those seeking the benefits of travel abroad will be opening up.

The various Skytrain and Skybus systems involve some patience on the part of the traveler. Either you buy your ticket in advance and wait to be told which day you wilfly, or you show up at 4 a.m. on the day wanderlust happens to hit you, and hope that the tickets hold out until you get to the head of the line. The fare can then as little as one-third of what the people with reservations pay.

However, an adjust fate has it that time is money, and if you can squander one, you probably throw around some of the other. The people who can't afford the regular air fare are kept to be the same ones who can't afford to take an open vacation, with a few day's leeway for getting off the ground.

It is for these people the new holiday package is intended. But it will also be the answer for people who want the status and fun of going to Europe without the annoyance of actually having to go to a foreign country.

Instead, you go to the nearest international airport and get in line with all people who are waiting in line to fly away. After all one of the joys of travel is supposed to be meeting interesting people. And those who have done extensive line-waiting, for super performances of art shows often end up saying that the fellowship of the line was the best part of the entertainment.

Occasionally, you might want to take breaks from that, as for instance when you find yourself at the head of the line with someone offering to sell you a ticket for someplace that wouldn't be nearly as much fun. Then you can wander off to sample the other attractions of the airport. The same type of fast food chains you will now find all over Europe have concessions in the airport. There will be bookstores to supply all that vacation-time reading. Postal cards and stamp machines for taunting those who are struck at home. And junk shops with souvenirs to remember it all by.

It should be an enriching, sociable and inexpensive vacation. And you get full credit for having roamed the world when you come home with tales of being stranded at the airport.