In some tourism circles it is considered bad taste - not to mention bad business - to tell travelers about unfawrable conditions developing in any area of the world. Except, of course, when circumstances make such a painful disclosure unavoidable. Armed revolt, earthquake or an epidemic, for example.

Fortunately, no such crisis is occurring in Mexico now and there is no reason for tourists to cancel plans for a south-of-the-border vacation. Indeed, the devaluetion late last year of the Mexican peso and reduced prices of hotel rooms, meals and some handicrafts have made Mexican - temporarily, at least - one of this hemisphere's best travel bargains.

Thousands of happy "gringos" and other foreigners have just retuned from their Christmas-New Year's holidays at jam-packed Acapulco or Cancun, where the wind and ocean were warm, the atmosphere peaceful, and the business quite normal.

Nevertheless, with due respects to the highly competitive and sometimes overly sensitive travel industry on both sides of the border, Mexico's internal problems have become a cause of growing concern to many U.S. tourists, including this good neighbor. There have also been signs of uneasiness in at least one segment of the U.S. travel trade, a cautious warning from the State Department and efforts to elicit from newly elected President Jose Hopez Portillo a reassuring statement to tourists about what action his administration plans to take.

Lopez Portillo has told one U.S. columnist that he has six months to restore stability. Inflation is rampant food prices have soared, and there is widespread unemployment and underemployment.

The Mexican travel industry, according to a UPI report last month, has been in the grip of its "worst crisis in history," with foreign tourism off by 12 per cent. Many blame the policies of former President Luis [WORD ILLEGIBLE] (This month might bring an upturn.)

An illinois travel agent was murdered last May while on a familiarization trip to Acapulco and another agent accompanying him is still missing. She is presumed dead.

On Christmas Day an elderly Illinois minister and his school-teacher daughter were shot to death in their car on a main road 80 miles east of Mazatlan. In this slaying nothing appeared to have been stolen.

The State Department's Office of Special Consular Services advised the American Automobile Association by letter last October that "the seriousness" of recent incidents "may be sufficient to warrant alerting travelers about the general situation." The letter stated that "there is no worry over the safety and well-being of the vast majority of tourists who travel to Mexico . . ."

The American Automobile Association, in a letter sent to President Lopez Portillo on Dec. 10, expressed concern "about certain hazards" that include "harrassment, assaults and armed robberies" and urged him "to do all that you can to eliminate these hazards and make travel into Mexico the rewarding cultural experience that it should be . . . " The AAA also noted that while serious problems "are relatively few in number, their impact is widespread."

How did Mexico find itself in danger of tarnishing its long-standing image as a safe country filled with warm, friendly people where the greatest danger - aside from reckless macho drivers - was the ever-present threat of hot chilis and Moctezuma's revenge? A people willing to overlook fractured Spanish and open their homes and their hearts to the North American visitor. A sunny land (albeit poor and often cruel to millions of peasants seeking to eke out a living), where the word gringo could shed its earlier unpleasant status of epithet and often, when uttered with a smile, lose even its occasional edge in a spontaneous burst of affection.

Certainly there are no simple or full answers. Furtunately, as syndicated columnist Jane Morse agrees, no indications of "anti-Americanism" have been found in any of the attacks on motorists or other travelers, and some of the cases publicized eleswhere a few months ago actually took place from one to two years ago (see related story by Morse on Page N2.)

Several of the more recent incidents have occurred in the troubled northwest area of Mexico, where militant peasant groups have been active. There are no racial or color conflicts in Mexico.

Yet former President Echeverria, it is generally agreed, made serious mistakes in his vain efforts to ingratiate himself with the Third World and thus secure the post of Secretary General of the United Nations (which he did not get), and in governing his country. Three of those mistakes are well known:

First, he aligned his country with the Arab-backed resolution in the U.N. that branded Zionism as "racism" just before the winter 1975-76 high season began. American Jews (heavy spenders in Mexico) and non-Jews responded with a very effective travel boycott that cost the Mexicans millions of dollars in lost bookings.

The rapprochement with Jewish travelers, begun belatedly by Echeverria before his term ended and continued warmly by his successor, may take a few more months to be fully effective, according to one high Mexican official who discussed the current tourism situation informally in a recent phone conversation. Tourism supplies at least one-third of Mexico's foreign exchange thus the "industry without chimneys" plays a vital role in the country's economic health.

Second, Echeverria's domestic programs and economic policies, coupled with the continuing adverse affect of Mexico's high birthrate and a world recession, prompted a devaluation of the peso shortly before he was to leave office. Though, among other results, the devaluation made Mexico cheaper for the tourist (and spawned an advertising and publicity campaign), it also upset the middle and upper classes and triggered a massive flight of captial from the country.

Third, in the midst of the unsettling monetary move, Echeverria complicated matters even more for Lopez Portillo by expropriating hundreds of thousands of acres of productive - and scarce - farmland from private owners and turning them over to landless peasants. This further alienated the private sector, which already distrusted Echeverria because of his radical policies; it also precipitated rumors of a military coup that threatened momentarily to destroy Mexico's peaceful image around the world, and it frightened travelers.

That move also has raised the hopes of militant peasants for more land and may yet cause serious peroblems for a new government aware that it has no land to give.

Little discussed, however, was a fourth mistake, which luckily has had little effect. This was Echeverria's appeal to nationalism that caused some Mexicans to dredge up decades-old (and often legidmate) gredges about past American intervention and injustices in connection with Mexico's internal affairs. More realistic Mexicans have long ago buried this past history with the knowledge that our common border and inextricably entwined interests make friendly relations an essential fact of life.

Certainly anything that might affect those relations, including further attacks on travelers, could cause a major disruption in tourism that might take years to repair, especially since the competition for the U.S. tourist dollar has greatly intensified during the past few years.

The AAA has just reminded its members "to be courteous and patient with authorities when traveling in Mexico, and to strictly follow all government regulations . . . automobile and recreational vehicle travelers especially should be prepared for roadblocks - many of them designed to block narcotics trade - and bureaucratic red tape that confront the ordinary American tourist in Mexico . . . .

"While at many places tourists can easily cross the border into Mexico, especially for short periods, it's important to remember that Mexico is a foreign country. It has its own laws, based on the Napoleonic code which presumes guilt, no innocence. It has its own methods of police interrogation. And there's little that American authorities can do to help out."

The AAA says this year "nearly 3.3 million U.S. citizens will travel into the interior of Mexico, spending an estimated $1.9 billion."

That's approximately 48 billion pesos, an investment certainly deserving of some tender loving care.

Rosenberg is Travel Editor of The Washington Post