Getting around the world in 80 days may have seemed pretty swift in its day, but did you ever hear of a Jules Verne character with jet lag?

Or, for that matter, la turista?

The latter, of course, has less to do with speed of flight than with eating and drinking when you get where you're going, but either can wreck a vacation or compromise a business or diplomatic mission. (What else but jet lag could put a president to sleep in the presence of a pope?)

According to Dr. Charles F. Ehret, a chronobiologist at the Argonne (Ill.) National Laboratories, people have to adjust their internal time clocks by one hour every day just by staying in the same place--people run on a 25-hour day instead of the planet's 24.

A slow adjustment of up to three or four hours a day isn't so bad, so it wouldn't be noticed on a slow boat to China, for instance. A fast jet is quite another matter.

But remember: You only get jet lag traveling east or west too fast. Period.

Canada geese, Ehret points out, fly almost completely north/south. Likewise, he says, the gray whale that swims from Alaska to Mexico, rarely dips into another time zone.

But people still determined to go east-west (the hardest to adjust to) and west-east can help their battered clocks to adjust, Ehret claims, by acknowledging these factors:

DIET: Because protein, carbohydrates and the methylxanthines (coffee, tea, chocolate) have varying effects on the brain and the body clocks, Ehret has come up with an exquisitely calibrated four-day feast/fast diet to precede takeoff. He also offers diet suggestions for either westbound or eastbound travel.

TIMING: Arrive as close to 8 a.m. (destination time) as possible. Try never to arrive between midnight and 5 a.m.

SOCIALIZATION: Sleep on the plane, exercise moderately when you awake and fit yourself into the daytime activities going on around you. It's easier to stay awake when you're involved.

Ehret's system for keeping jet lag in its place appears in his book, Overcoming Jet Lag (Berkley, $4.95), which also contains travel hints for such situations as special needs of the elderly or for those taking certain medications.

Although Ehret's system has never been tested scientifically, he has testimony from thousands of military and industrial executives who have used it in the past few years.

For a wallet-size card describing the Argonne Anti-Jet-Lag Diet, write Dr. Charles F. Ehret, Argonne National Laboratory, 9700 S. Cass Ave. Argonne, Ill. 60439.

Dr. Martin S. Wolfe, a specialist in tropical medicine and parasitology, is more concerned about the nasties laying in wait for you. He has picked up where the Public Health Service left off a few years ago and is providing advice, immunizations and laboratory analyses for people about to travel to parts far away and for those who have brought back unpleasant internal beasties and assorted afflictions acquired elsewhere.

A former State Department expert--he accompanied Henry Kissinger during his days as the world's most peripatetic diplomat--Wolfe now works as a consultant for State, the World Bank, the Peace Corps and other international institutions. In his private Traveler's Medical Service, he devotes a great deal of time to what he calls an "immunological virgin," the occasional, usually vacationing traveler.

Wolfe and his staff keep a day-by-day record of which disease may be breaking out in what countries so that only those immunizations required need be administered, and no one will go off without necessary immunizations.

"People," he says, "are going more and more off the beaten track, getting into places that only seasoned travelers got to 10 years ago."

There is also the problem of "some people taking prophylactic preventive drugs in excess, taking potentially dangerous drugs when they don't really need them. You have to tailor recommendations to the person's itinerary."

Such as: "You have to be careful that a person going to India or Pakistan or parts of Southeast Asia won't be stopping in Africa, because if a plane so much as touches down in Nairobi, for example, Indian authorities might deny entry without evidence of a yellow fever shot." This could leave the traveler with the unpleasant options of being quarantined or aborting his trip and going back on the next flight.

Some health hazards are limited to particular countries and sometimes, as is often the case with malaria, for instance, to certain parts of many countries.

And sometimes individual countries, or areas, have specific hazards. The sobriquets for traveler's diarrhea--such as "Montezuma's revenge" or "Delhi belly"--often are hints about where they may be encountered.

Then there are hazards either so widespread or so serious, that some preventive measures are recommended by travel-medicine specialists like Dr. Wolfe.

Some examples:

* POLIO: Although polio vaccine is used almost universally in this country and its incidence is very low, it still appears in many parts of the world. People who have had the series and one booster are considered to have a lifelong immunity. Others should be completely immunized.

* DIPHTHERIA AND TETANUS: Immunization should be renewed every 10 years.

* YELLOW FEVER: Shots available only at specific centers--Wolfe's is one--because of its perishability. Generally recommended for travelers to tropical Latin America and much of Africa. The shots last for 10 years, may not be given to pregnant women, infants or people allergic to eggs.

* CHOLERA: Shots not recommended, largely because they don't work very well. "In a sense we try to discourage cholera shots unless it is being required by countries near other countries experiencing outbreaks."

* HEPATITIS: Doses of gamma globulin before traveling in tropical areas and in places with poor hygiene can almost completely protect against the hepatitis-A virus. Not usually recommended for children under 12 because the virus generally causes only mild symptoms in younger children.

* MALARIA: "This is a killer, and it can be prevented." Malaria occurs wherever mosquitoes abound, uncontrolled, especially in tropical areas. Drugs that usually prevent it: chloroquine alone or, in areas where the parasite has become resistant, with a long-acting sulfa compound called Fansidar.

Important to begin the drug (or drugs) in weekly doses one week before going into malarious areas and continue it for four to five weeks after leaving. The drugs may have side effects and should not be taken by pregnant women.

"It is also important to know that some cities, even in Asia and Africa, are free of malaria; that malaria mosquitoes bite only in the evening-nighttime hours and that even young infants need to be totally protected, even with the preventive drugs. After all, it only takes one bite . . ." (And don't forget insect repellents.)

DIARRHEA: This bane of the casual traveler can be caused by bacteria, virus or parasite. Usually more annoying than disabling. Preventive doses of a drug called doxycycline may help, although it can itself cause stomach upset, sun sensitivity and is effective only against bacteria, including E-coli, the main culprit in traveler's diarrhea.

Large daily doses of Pepto Bismol (only the liquid, not the tablets) have been found to be an effective preventive, and can be used successfully against a moderate episode. Lomotil, for which a prescription is needed, is a strong anti-diarrhea drug, but can cause drowsiness.

Smallpox vaccinations are no longer required for reentry to the United States. The disease has not been reported anywhere in the world for about five years. The risk of the shot is greater than the risk of the disease.

Because parasitic infestations may not show up until after the traveler returns home, Wolfe recommends a routine screening on return from countries where, like Mexico, sanitary conditions may be poor, water questionable and crops, including lettuce and root vegetables irrigated with "night soil," or untreated sewage.

Wolfe advises against drinking alcoholic beverages on long airplane flights, but recommends the consumption of other liquids.

(The dehydration often experienced by air travelers--with its attendant lightheadedness and irritability--is caused by high speeds and altitudes, not jet lag as many believe.)

For further information: Dr. Martin Wolfe, Traveler's Medical Service, Suite 408, 2141 K St. NW, Washington D.C. 20037. 466-8109.