They can be seen everywhere in the cavernous corridors of the Agrarian Reform Ministry - swarms of sad-eyed peasants who have trekked to the capital in hopes that the pilgrimage will magically satisfy their craving for land.
Some will remain for days, patiently unrolling straw mats to sleep on and filling the halls with the odors of unwashed feet and of tamales andchili peppers bubbling in pots of hot water.
Occasionally, a harassed official will emerge to talk with them. But it is a dialogue of the deaf. The bureaucrats' legalistic explanations of why nothing can be done elicit only uncomprehending stares from the illiterate peasants.
Eventually, they will leave and drift back to their villages. But there are always others to take their places in an unending cycle that underscores why the hunger for land is the most constant and insoluble of the many problems plaguing Mexico.
Sixty years after the Mexican Revolution, the ghosts of Emilliano Zapata and Pancho Villa are stirring again. In the northwestern states of Sonora and Sinaloa, a contiguous farm belt that is the country's most fertile region, peasants and landowners have been locked in a confrontation that, for a time, seemed to make another land war as imminent as the jerk of a single itchy trigger finger.
The trouble began in mid-November, when former President Luis Echeverria, on the eve of leaving office, expropriated about 247,000 acres of privately owned a farmlands in Sonors - an area six times the size of the District of Columbia.
Echeverria's move started a chain reaction in which thousands of peasants and migrant workers seized and laid claim to huge chunks of other private farms in a broad swath cutting south hundreds of miles through Sinaloa.
The tensions generated by the squatter invasions have been temporarily tamped down by the energetic efforts of Mexico's new president, Jose Lopez Portillo, and his agriculture minister, Jorge Rojo Lujo. They have persuaded the two sides to back off and allow the tangled dispute over land ownership to be resolved by the Mexican courts, a process that could take months or even years.
While this time-buying agreement averted an immediate crisis, it offered no real solutions for Mexico's long-range land dilemma.
As Lopez Portillo recently remarked: "The land is not made of rubber. It is not elastic and cannot be stretched indefinitely."
In all of Mexico, there are only about 80 million acres of arable land. Only slightly more than half of it can harvested regularly. Yet, the country retains an inherently rural outlook in which more than 40 per cent of its 62.3 million people cling to the land and earn their living from farming.
Among Mexican peasants, devotion to the land is almost religious. It feeds on the mythology of the revolution, with its stories of how millions of peons fought to free themselves from serfdom on great estates owned by a handful of absentee landlords.
The sweeping agrarian reform that emerged from the revolution was intended to break up permanently the big estates and make small plots of land, worked by peasant families, the backbone of the Mexican agricultural system.
The core of this system was the ejido, a tract of land owned by the government but divided into sections of up to 50 acres each for farming by individual peasants. More than 70 per cent of Mexico's farmland is under the control of some 30,000 ejidos.
Of all the ideological totems created by the Revolution, thte ejido is the most sacrosanct. The Institutional Revolutionary Party, which has controlled Mexico for almost 50 years, is heavily dependent on the support of the ejiditarios, as the members are called.
"The ejiditarios are organized primarily to vote and only secondarily to produce," a former agriculture minister once said in an indiscreet but accurate assessment of party attitudes.
The system is riddled with flaws that have turned its original intentions into a shambles. For one thing, there is not enough land to go around, and at least 4 million peasants who live on the soil still have no land of their own. That is what causes the Agrarian Reform Ministry to be under continual siege by the procession of peons from every corner of Mexico.
The government's only options are to turn the disappointed land seekers away with vague promises of some future reward or, when the frustrations seem on the point of boiling over, to open a temporary safety valve by carving the available land into ever smaller plots, as in Sonora and Sinaloa.
But, such tiny units cannot take advantage of the efficiency that modern technology makes possible for largescale farming. Most have never been provided with the credit, machinery and technical assistance necessary to make them work effectively. Even when such aid has been available, superstition and lack of education have made peasants reluctant to do things differently than in the time of their fathers.
As a result, most ejido plots have not provided their occupants with anything better than bare subsistence. Many ejiditarios, finding that they are no better off than their grandfathers in pre-revolutionary days, simply abandon their plots or rent them illegally to others.
The failure of the system is underscored by the statistics. Although 40 per cent of Mexico's people are engaged in agriculture, they produced only 10 per cent of the country's gross national product during 1975; and the country has switched in recent years from being a net exporter to a net importer of agricultural products.
The 20 per cent of Mexico's exports that are agricultural are almost totally produced by the country's privately owned farms, not by the ejidos . Such farms are still permitted, but the law limits them, in areas of irrigation, to individual holdings of 250 acres.
The government charged that land owners in Sonora and Sinaloa disguised their huge estates by registering the inter-linking, legal-sized plot in the names of women and children not actually working the land, as the law requires.
There are also many other private farms that, while not big estates, exceed the 250-acre limit. The results of brothers or other relatives pooling and working their holdings together as joint enterprises, they are the type that have largely been the targets of squatter invasions.
While the big and medium-sized farms may or may not be legal - a question that the courts must unravel - they are nevertheless the most productive holdings in Mexico.
Carlos Castro, the youthful general manager of the private farmers' association in Sinaloa, noted that in his state 77 per cent of the farmland is controlled by the ejidos and 23 per cent by private owners. Yet, the large mechanized private farms produce 66 per cent of the total value of crops in the state, including every penny of the $200 million worth of winter fruits and vegetables exported from Sinaloa to the United States last year.
"Our members," he charges, "are being penalized for being efficient - for doing what the ejidos failed to do.
"There are 230,000 privately owned, irrigated hectares (approximately 575,000 acres) in Sinaloa," Castro says. "If you divide them up into ejidos and give each ejido member 10 hectares - not even the 20 to which he is technically entitled by law - you would benefit 23,000 hectares now give jobs to 150,000 heads of families."
It is not quite so clear-cut as that, since many of the jobs that he cites are seasonal and leave the people who work on private farms unemployed for long stretches of each year.
Still, his logic seems irrefutable. Mexico is not going to solve the problems of its rural population by trying to create more small farming plots out of land that is not there. Nor is it going to make itself more self-sufficient in agriculture and produce more dollar-earning exports by carving up the few efficient farms it already has.
Lopez Portillo, a former finance minister, obviously understands this. But any solutions that he does attempt must proceed from the assumption that the ejido is an emotionally ingrained part of the Mexican fabric and will remain the basis of the agricultural system for a long time.
This will probably mean a new drive to turn the ejidos into collective farms - to make them emulate the private farms by working the ejido land as one large, centrally directed enterprise rather than as a collection of individual peasant plots.
The idea is not new. Successive Mexican governments have been urging it for 20 years. Echeverria gave especially high priority to experimenting with ejiod collectives.
So far, though, the idea has failed to take root. To make it work will require great patience and a far greater commitment of money and resources than the government, with its past emphasis on industrialization, has been willing to spend.
Given the realities both of Mexico's politics and its available land resources, it seems the only possible way to ease the plight of the peon and the centuries of hardship that have resulted from his mystical attachment to the soil.