Viasa Flight 970 left an hour and a half late this morning, which means that it left right on time.

The weather was perfect, the big orange, blue and silver DC-10 was at the gate all the while and, of course the passengers had been at the airport for several hours -- because in Caracas, as elsewhere in South America, passengers are required to appear 90 minutes before scheduled departure time or risk being told they are too late, no matter now many hours later the flight actually leaves.

This morning we sat patiently waiting for Flight 970, buying duty-free cigarettes and perfume, reading newspapers and novels, or simply trying to sleep a bit as the clock moved closer and closer to noon. Finally Viasa decided the time had come to board the DC-10 and, minutes later, Venezuela's Caribbean shore was nothing more than a memory.

We climbed to 37,000 feet and what is normally the worst part of flying in South America, the trip to the airport, the long wait to check in and the even longer wait to board the plane -- any plane to anywhere -- was behind us. Gracias a Dios, we were on our way.

As I am writing this, Flight 970 is somewhere over the Amazon Basin on its way from Caracas to Santiago de Chile.

A rather good lunch of ham Britannia (where the names for these dishes come from is beyond understanding), filet of beef Mexicaine, green peas, salad, cheese and almond cake has already been served.

The crew is friendly and the flight has been routine thus far. The air conditioning was dripping water all over the aisles before we got airborne, though, and I am dying to know why a steward passed by not long ago carrying a toilet seat.The movie that was to have been shown has been cancelled without explanation but, all things considered this is the best Viasa filght I've ever been on.

Flying in South America is still a adventure: sometimes luxurious an flawless but usually fraught with the unexpected. I will never forget the time a Lan Chile flight I was suppose to take left 45 minutes early. Nor the time I sat freezing in La Paz waiting for an AeroPeru flight to Lima, which left four hours late (at 2 a.m.) because the winds were so fierce that the plant couldn't land.

Half the time, fights are not announced and one is expected to some how sense when the time has come board. On the other hand, the woman who announces departures at the Rio airport is terribly efficient and must have the sexiest voice in the world.

In general, though, attempting to get by air from one part of South America to another is such a hassle that one wishes for the bland, impersonal but efficient service of U.S. carriers like American or United. Unfortunately, neither has yet found its way to this part of the world. The United States is represented by Braniff and Pan Am.

Even the shortest hop in South America is an all-day affair. The flying time between Santiago and Buenos Aires is about one hour and 45 minutes, for example, but from door to door the trip usually takes about six hours. It is a 45-minute trip from downtown Santiago to the airport and you must arrive at least an hour ahead of departure. On a good day, the plane will leave only an hour late. It takes at lease half an hour to get through customs in Buenos Aires and another hour, at least, to get into the city. You will have wasted the better part of the day.

Since I began flying regularly above this continent over a year ago, I think I have traveled aboard at least 80 percent of the major airlines that fly down here: Braniff, Pan Am, Viasa, Varig, Cruzeiro, Avianca, AeroPeru, Aerolineas Argentinas, Lloyd Aereo Boliviano, Pluna, Guyana Airways, Faucett, Lufthansa, Air France and probably a few more I've put out of my mind.

I have tried twice to fly Lan Chile: Once it left early and I missed it. Once the plane was five hours late (Buenos Aires to Santiago) and I took Braniff instead. So far, I have missed Ecuadoriana and Lineas Aereas Paraguayas but, given the business I'm in, I'm sure I will have the pleasure sometime in the near future.

Although it is uaually impossible to choose the airline you fly in South America because the number of flights, even between major capitals, are so few and connections so bad, there are times when it is possible. The airlines are clearly different and, in this consumer age, Americans should at least know what they are in for when they board their flights between, say, New York and Buenos Aires of Bogota and Rio.

Here then is a very personal guide to the airlines of South America -- in case you happened to have a choice. Buen Viaje, as they say.

VARIG: Generally considered the best airline in South America and one of the best in the world. From the champagne served in real stemware before the plane even leaves the ground (on domestic flights) to the excellent meals served on any Varig flight, Brazil's national airline is superb. Thoughtful little touches, like toothpaste and toothbrushes on overnight flights, almost make up for the fact that Varig flights are usually so crowded that it is rare when there is extra room to stretch out on the longhaul service from Rio to New York or Europe. Still, Varig combines the gracious style of the Carioca with the efficiency of the Sao Paulista to make it the airline of choice in South America -- whenever a choice is possibile.

AEROLINEAS ARGENTINAS: One of the best things Argentina's military government did when it came to power three years ago was put an air force general in charge of Aerolineas. What was once a dreadful excuse for an airline rivals Varig for tops in South America and is now probably among the top 10 in the world. The planes are new, the service good, the food not bad at all and, except for the fact that Argentinians break into applause when an Aerolineas flight lands in Buenos Aires, Aerolineas is a real pleasure to fly. It is especiaily worthwhile flying with Aerolineas when your destination is Buenos Aires because Argentina's national airline has its own terminal at the airport, which saves a lot of time getting through customs.

VIASA: It is usually impossible to get a confirmed seat on a Viasa fight because Venezuela's national airline doesn't usually answer telex requests from anywhere else in South America except Caracas. Except for their DC-10s, Viasa's planes are uncomfortable because they try to sequeeze in as many passengers as they can.

LAN CHILE: A friend of mine whose judgment I respect says Lan Chile's food and service are actually quite good if you ever manage to get aboard. The problem is that Chile's national airline is overextended: Its routes stretch from Santiago through South America to the United States and Europe but Lan simply does not have enough planes. Therefore, its flights are almost always way behind schedule, except for the one I tried to catch from La Paz to Santiago, which left early. (Lan Chile's central office in downtown Santiago couldn't believe it when I complained and they offered their apologies after they checked.) Fxcept when taking Lan from Santiago, its home base, you may be at the merey of the weath far away in New York or Europe, where so many of Lan's planes start out on their way home to Chile.

AIR LLOYD BOLIVIANO: Getting into and out of La Paz is always an adventure no matter what airline you are on. It always seems as if you are about to land on the moon. My sense of it is that the airport at La Paz is tricky, and Air Lloyd Boliviano has the most experience. But Air Lloyd is usually late -- often days late -- and the food is, now shall I put it, simple. The Bolivians do try, though, and they are nice to passengers.

PLUNA: Not bad, not bad at all. But Pluna, Urguuay's national airline, basically files between Montevideo and Buenos Aires or Brazil, which means that most Americans would not have the occasion to fly it.

FAUCETT: Peru's domestic alternative to AeroPeru. Quite good and far preferable to the state-owned competition. From Lima to Cuzco and Machu Pichu, take Faucett.

CRUZEIRO: Varig's cousin and almost as good. Cruzeiro, which flies mostly inside Brazil although it does have some international routes, is quite respectable and worth trying.

GUYANA AIRWAYS: There is no choice inside Guyana and plenty of alternatives to Trinidad. Guyana Airways is for those people who collect airlines -- that is, who love to fly exotic lines their friends haven't yet been on.

AIR FRANCE, LUFTHANSA, IBERIA: Unless you can go with Varig or maybe Aerolineas, the European airlines are far and away the best flying in South America. It is often possible to fly the Europeans between major cities and they are highly recommended. Another advantage is that Air France, Iberia and Lufthansa almost always fly jurnbos in this part of the world -- which means greater comfort and better service. CAPTION: Illustration, no caption; Picture, Rio de Janeiro.