POLITICS AND WAR have a way of affecting the free flow of tourists--so it's now adios Buenos Aires and Havana (and Est-ce-que vous allez a Paris?).

U.S. travelers considering taking vacations in either Argentina or Cuba have been told by the federal government they should make other plans. Asi es la vida. The warnings were given recently by the State Department and the Treasury Department.

The following travel advisory was issued in Washington by the State Department (at this writing, a cease fire was being discussed--obviously, if a durable agreement materializes, the advisory will be canceled):

"Due to increasing tensions between Argentina and the United Kingdom, the Department of State advises U.S. citizens to avoid travel to Argentina at this time.

"U.S. citizens who find it necessary to travel to Argentina and those resident in Argentina are strongly advised to register at the American Embassy, 4300 Colombia Ave., Palermo, telephone 774-7611."

Certainly there have been no threats against American visitors and this is merely a matter of sensible caution in a "war zone." We can hope there'll soon be peace on the pampas.

In another of its periodic travel messages, which is less ominous--but certainly no less urgent to lovers of Paris in the springtime--the State Department noted: "The American Embassy in Paris reports that because of the Versailles summit meeting and important international trade fairs this summer, most hotels are already fully booked between May 16 and June 15. Visitors should have hotel reservations confirmed in advance of arrival." The French Government Tourist Office in New York confirms the warning.

Meanwhile, the Treasury Department has again lowered the boom on vacation and business travel to Cuba. Effective yesterday, the department banned most such visits in a move that apparently is designed more to send Fidel Castro a clear signal of U.S. disapproval of his foreign policies than to strongly affect Cuba's economy.

Treasury has prohibited American citizens from paying for business or vacation travel expenses within Cuba with credit cards or currency. Exempt from the ban are Cuban-Americans who have close relatives in Cuba, "bona fide" researchers, journalists and government officials, said a Treasury official. Also, the department will issue special travel permits to those proving their trip is being made for "humanitarian reasons," public performances, exhibitions, etc.

Naturally, travel agents are permitted to make necessary arrangements for those with exempt status, but they are not required to ascertain whether each passenger is, indeed, qualified to make the trip. Treasury is expecting voluntary compliance--particularly since anyone violating the ban can be prosecuted under the Trading With the Enemy Act, with penalties of up to 10 years in prison and a fine of up to $50,000, or both.

But how do the exempt visitors manage to pay for accommodations, food and services while on the island? There's no problem, according to Ray Konan, chief counsel of the Treasury Department's Foreign Assets Control Office. They can buy a package that includes air fare, accommodations and some meals before going, or they can use cash, travelers' checks or personal checks in Cuba to pay for hotels, food and necessities as usual.

A Treasury spokesman agreed that, though the Reagan administration is seeking to reduce the flow of dollars to Castro, thus complicating his efforts to finance rebels in Africa and Latin America, the travel ban will not be a major blow to Cuba's economy because 60 percent of some 38,000 Americans who visited the island last year would be exempt from the new restriction.

Despite hoopla in recent years from a few eager capitalistic entrepreneurs on both sides of the Straits of Florida, it seems that there is no hope of an early resurgence of U.S. tourism to an island once called the "Pearl of the Antilles." While a trickle of visitors enjoyed the elaborate shows at the Tropicana nightclub in Havana and the warm sands of Veradero Beach, and got a close-up view of the revoluc,ion, the tourism experience received mixed reviews and Cuba never became a serious competitor of major Caribbean resort areas like the Virgin Islands, the French and Dutch islands, Jamaica, Haiti and the Dominican Republic.

The original travel ban that ran from 1963 to 1977 was rescinded by then-President Carter, who had hoped the move would foster better relations between this country and Cuba. It failed.

Though I have made trips to Havana in the past, I have refused to spend my dollars on present-day vacations there until full diplomatic relations are restored between this country and Cuba. Without that, the "Pearl" has little chance of again becoming a tourism jewel.