This was the year we had planned to have a French vacation. And this was the year the franc dropped to less than four to the dollar and never rose much above that. Two years ago when we spent a three-week vacation in France, the franc was almost five to the dollar and there had not been two years of double-digit inflation. Even then it was one of the most expensive countries in Europe.

We have just come back from another three-week stay in France. To our delight, we spent not quite 10 percent more than two years ago, and had at least 10 percent more fun. With some effort and imagination perhaps you will do even better.

The cardinal rules still apply. Never travel during the season. That means during the summer. Always travel lightly, never more than two bags which can be hanled without porters, bellhops and the need for taxicabs. And to the fullest extent possible use drip and dry clothing.

The airfare was no problem. In some cases it was as low or even lower (depending upon the plan) than two year ago. With rising fuel costs, however, rates could increase quickly. Forget about renting a car. The best bargin in Europe is the railroad.

The French National Railway pass can be purchased in America with American dollars: $200 for 15 days. It includes roundtrip first-class transfer from one of the Paris airports to downtown Paris via either the Roissy-Rail or Orly-Rail. This is a savings of $10. Plus seven free days on the Paris metro and bus systems, a savings of $14, and free admission to the great new Pompidou Museum, a savings of $3.50. As an extra, it also entitles you to a self-drive car for one day (two days for a couple) for up to about 60 miles of travel each day. But more important, you can travel first class, even on the famous high speed T.E.E. trains, anywhere in France. Another bonus gives you special discounts on bus excursions run by the French railroads.

The railroad pass, alone, we conservatively estimated, saved us more than $300. Besides, it made travel simpler. No need to buy tickets -- merely jump on the train. The trains are modern, restful and give you a marvelous opportunity to see the country and meet its people. In some cases we brought a picnic lunch with us, in other cases we ate on the inexpensive grill car when there was one. Avoid the diners, an easy way to save $25 or more a meal.

Currency exchange can be unncessarily costly. Buy your francs in France and whenever possible in a large bank. You can lose up to 10 percent if you exchange dollars at your hotel or a restaurant. As for traveler's checks, Cooks and Barclays are free and are recognized and convenient to use. However, there is no need to tie up much money in checks. We use all the major credit cards. In that way we are always certain to find a restaurant, hotel or store which will accept our cards. The exchange rates of conversion by the credit card companies are fair, and you do not have to be concerned about exchange fluctuations or about keeping a supply of francs on hand. But more important, you are billed one month, two months and even longer after you use the card. This amounts to interest-free financing of your trip.

Hotel rates have risen considerably. In many cases the continental breakfast is no longer included. But rather than spend the $5 or more for the hotel breakfast, you can always find a nearby cafe where the croissants and beverage are half the price. We always bring with us packages of dry American cerals, oatmeal or cream of wheat, and some packages of Tang or equivalent. Hot water is free and there is always extra milk. Ask for an extra cup and glass. Voila! An American breakfast at less than American prices.

One advantage of traveling by railroad, unlike in America, is that you can always find good inexpensive hotels near the stations. For instance, in Paris, Strasbourg, Toulouse and Bordeaux, we stayed in hotels either in or adjoining the stations, eliminating the need for expensive taxicabs. In those areas there was no probem with noise (trains are electric), and in rooms with air conditioning we could close windows. Stations are centrally located and not surrounded by deteriorating neighborhoods.

We always travel with a small transister radio. It is fun to pick up the European stations and you do not have to worry about getting a hotel room with a radio or television. In most cities you can easily pick up the Voice of America or the British Broadcasting Corporation (BBC). No need for the Herald-Tribune or the European edition of Time. Again, the savings in francs are considerable.

The price of food is high in France. We've discussed breakfast. For second meals we often brought fruit, cheese, cold cuts, bread, wine and yogurt at a local market. That way we never felt guilty or extravagant about having a few meals a week at a choice restaurant. Whatever the price, the meals at a Michelin-starred restaurant are always a worth-while experience. For two or three hours in an elegant ambience you are wined and dined and fussed over. It is great food plus entertainment. As for tipping, no need to play the prosperous American -- gratuities are included in your bill. Do as most Europeans do: If you like the service, leave token tips, a few francs.

A word about the drinking water. The French have a fetish about using tap water. At a dollar and a half or more for a bottle of mineral water, it is a fetish you can ill afford. The water in France is pure and wholesome, and we never had any ill effects from drinking it. Also, a suggestion about the wine: The house wine is generally excellent and a fraction of the cost of the so-called vintage wine. If you must have the corked wine, stick to the wine of the region.

As for shopping, here you can save a bundle. Do not do any. Most products are cheaper in America. If you must have French perfumes, gloves and similar luxury items, there are a few well-known establishmens in Paris which give 25 percent discounts, plus forms which you present at Customs when you leave and the stores mail you back 15 percent -- the Value Added Tax. (Not all stores will refund the VAT, so you might want to ask first.) There is no local sales tax and the savings in some cases amount to more than 50 percent of the New York or Washington prices. With the new $300 per person U.S. Customs allowance, you should have no tax to pay on purchases this year.

Just one last item. In lieu of post cards, say goodbye to your friends before you leave and promise to show them your slides when you return. Airmail postal cards will cost you almost three francs a card (about 75 cents). With a large family and many friends, that can amount to the price of your first night in Paris. Or a meal at a three-starred restaurant!