Mexicans have developed an incredibly rich vocabulary to describe the corruption that so pervades their country that some people joke about living "in what must be the richest place in the world because it supports so many criminals."

Soborno (graft); cohecho (bribe); >mordida (payoff); vendeplazas (job selling); igualas (covert payments to reporters); gacetillas (stipend to editors to publish specific articles) and aviador (person who is paid without working) -- these words are part of this nation's lengthy lexicon of corrupt practices.

Corruption in Mexico touches everyone, from the equipment salesman forced to pay a kickback to the company purchasing agent to the taxpayer incensed by ex-President Jose Lopez Portillo's moving into a posh, five- home compound on 71/2 acres outside the capital. "It doesn't matter if they steal a bit," said a taxi driver who is used to forking over mordidas to policemen for real or fictitious traffic infractions, "but they shouldn't steal so much."

That is why, in his campaign of "moral renovation," Mexico's new Harvard-educated president, Miguel de la Madrid, has begun cracking down on the centerpiece of Mexican corruption, its oil industry.

A number of former officials of Pemex, the state oil company, have been charged with corruption. And Mexico's attorney general last month accused Sen. Jorge Diaz Serrano, former head of Pemex and architect of Mexico's oil boom, of participating in a $34 million fraud in the purchase of two natural gas tankers. The attorney general has also been asked to investigate what happened to 317 million barrels of oil that Pemex and other government agencies cannot account for.

But the real test of de la Madrid's anti-corruption drive is whether it takes on the 110,000-member oil workers' union (STPRM), which is in a class by itself when it comes to shady activities.

A wide array of charges have been leveled against STPRM's leaders by former union officials, by the leader of the National Petroleum Movement (a reformist element within STPRM), and by investigative reporters for such publications as the magazine Proceso and the daily newspaper Excelsior.

While nominally just another labor organization, the union and its 29 locals not only boast an effective political apparatus but also business offshoots that include the posh Alameda Hotel in Mexico City, oil drilling concerns, construction companies, huge farms, credit unions, supermarkets, hospitals, swimming pools, gymnasiums and funeral homes.

Nobody begrudges the union the right to amass wealth and influence. But evidence is accumulating that this wealth has been built on illegal activities which, in many cases, have taken money from the pockets of rank and file workers to enrich union big shots. Under its contract with Pemex, the union recruits virtually all non-management employes of the oil monopoly. Union leaders use company property for their own purposes and take a "bite" out of the checks of the aviadores, people who don't work but show up to collect their "wages" on payday anyway.

During a dozen trips to Mexico in the last six years, I was also told by more than five persons intimately familiar with the Pemex union that retired petroleum workers are required to labor on union farms or risk the loss of their pensions. Petroleum engineers fork over thousands of dollars to the union for a lifelong position; temporary secretaries sometimes pay for their jobs with sexual favors, according to a Pemex employe in Villa Hermosa who told me he knows this from the other Pemex secretaries he dates.

Even in death, workers must satisfy the union's insatiable appetite for tribute. Last April 11, a Proceso story reported how the oil workers local in Poza Rica deducts the equivalent of 105 days' wages from death benefits to pay for elaborate funerals of deceased Pemex employes. Among other things the money goes to pay for unnecessary autopsies -- still another opportunity for mordida. Dr. Ignacio Espinosa Solis, a forensic physician, explained in the article that union leaders own the undertaking establishment which handles the bodies.

Pemex contributes an amount equal to 2 percent of all its investment to the "social works" of the union. This totaled $220 million between 1976 and 1982. Undeniably much of this money went to projects that benefitted union members, such as housing, sports complexes, schools and health clinics. However, former union activists interviewed in the past two years have questioned whether all those funds are directed to the projects.

The press in Mexico City regularly comments on the affluence of senior union officials, including the fondness of some of them for large homes, private airplanes, jewelry and trips to Las Vegas gaming tables.

How union officials accumulate such affluence has never been documented in detail. What is known is that some top officials have formed companies in the name of their locals to take advantage of a Pemex concession, first granted in 1977, awarding the union 40 percent of all onshore drilling contracts.

According to two senior engineeers, both now retired from Pemex, this set-up enabled the union companies to subcontract the drilling and pocket commissions in the process. In some places, such as in Poza Rica, union companies collected commissions from Pemex on wells that were needlessly drilled. The stakes in the Pemex-union deal on drilling can be seen by the fact that Pemex spent nearly $4.5 billion for onshore drilling between 1977 and 1981.

These drilling contracts are centralized in the National Commission of Contracts, headed by Joaquin Hernandez Galicia, known by friends and foes alike by his childhood nickname, "La Quina," a diminutive of his first name.

Although he has not formally headed the union since 1964, La Quina is the undisputed power within it, and therefore, one of the most influential men in Mexico. According to union officials, La Quina continues to place his loyalists, such as current president Salvador Barragan, in key union posts.

"Not a leaf falls without his knowledge," a current union official told me.

Born into a humble union member's family, La Quina began work in Pemex as a welder. He soon became interested in union politics and fought his way to the top of his own local before capturing the national presidency in 1962. He then used his position to forge a nationwide alliance that has allowed him to hold sway over Latin America's strongest union to this day.

In a union worth billions of pesos, La China keeps tabs on the disbursement of every centavo. He personally approves credit union loans to members of his local and grants favors to followers who congregate outside his home three evenings a week. "He decides everything, reassignments, promotions, leaves, commissions, contracts. . .," said a member of his entourage.

According to former Sen. Samuel Terrazas Zozaya, who headed the oil workers union in the late 1960's and subsequently broke with La Quina and attempted to execute reforms, new union members put their signature at the bottom of a blank piece of paper, which can be filled in later for any purpose the union bosses stipulate.

Unlike some of his more showy sidekicks, he dresses simply, limits his jewelry to a cross worn around his neck, and presents himself as a modest man of the people. He resides at an unpretentious home outside the Gulf Coast town of Ciudad Madero. When I interviewed him there several years ago, La Quina scoffed at the idea that he personally was involved in any wrongdoing.

As one of his armed bodyguards looked on and a 30-30 rifle lay on a coffee table between us, La Quina casually identified corruption as the union's number one problem. Slowly sipping a glass of papaya juice, he pledged to battle for the "internal cleanliness" of his organization by expelling from the union anyone caught selling jobs. He acknowledged that about one ouit of five of the oil industry's temporary jobs were then being sold.

More recently, La Quina has responded to critics by accusing Pemex's current administration of "wastefulness, bureaucratism and incompetence," denouncing a "plot" to assasinate him, threatening to retire from all union activity in 1984 and attacking his critics in the press.

La Quina's statements notwithstanding, union practices continue to raise questions.

According to a detailed article in Proceso last April, the leaders of the union local at Poza Rica purchased Chichicuatla Ranch in the state of Veracruz and stocked it with 2,700 head of cattle as their contribution to then President Lopez Portillo's plan to stimulate food output. But a subsequent examination of land records revealed that, contrary to the union's assertion, title to the property was in the name of a former secretary general of the union and his associates rather than in the name of the local, according to Proceso.

The magazine also reported that only 270 of the 2,700 cattle were listed as union property in the public property register. The article said the others belonged to non-union friends of the former secretary general.

One of La Quina's bitterest enemies and critics, Hebraicaz Vazquez Gutierrez, who founded the National Petroleum Movement in the early 1970's as a reform element within the union, charged in an interview with me in 1978 that union leaders back up their enrichment schemes with force.

Vazquez, who had served as a local union official, claimed the union uses some 3,000 armed men, who are on Pemex's payroll, to repress dissidents and whip up support for union ventures. Vazquez's efforts at reform ended in failure. He was subsequently arrested on a charge of being involved with a guerilla movement, and jailed. Vazquez has been unable to get his job with Pemex back, but his friends have sent petitions to the new Mexican government requesting his return to the job.

More sensational was the gangland-style killing in 1977 of Heriberto Kehoe Vincent, the head of a union local who broke with La Quina. The assasin was killed a few minutes afterwards and no link to the union leadership was ever made.

That STPRM does some good things for its members is undeniable. Encuentro, a local English-language publication, reported on April 28 that it takes nine workers to produce a barrel of crude in Mexico compared to l.5 workers in Venezuela and the United States. Such featherbedding may be a credit to the power of the union. At least, it can be argued, it is providing jobs in a country of chronically high unemployment.

But the union still only employs 110,000 workers in a country in which nearly half of the work force is either out of a job or employed only sporadically. At a time of economic austerity brought on by declining oil revenues and an $85 billion foreign debt, such inefficient practices are a sea anchor on an economy that still is doing little for the millions who live in poverty.

Why hasn't the government cracked down on the chieftain of the "petroleum jungle," as journalists describe the oil industry? To begin with, labor is the sturdiest pillar of the ruling Institutional Revolutionary Party (PRI), and the oil workers energetically mobilize funds, crowds, and votes for favored candidates at all levels. An ability to deliver support won La Quina easy access to the presidential palace under Lopez Portillo, who left office eight months ago after presiding over what several newspapers called the most corrupt administration in modern Mexico.

Moreover, displacing La Quina and his disciples might only bring in a new generation of STPRM leaders every bit as self-serving as their predecessors -- but perhapssnot as slavishly devoted to the PRI.

Also, cleaning up the union could reveal the ubiquitous wrongdoing within Pemex itself.

De la Madrid claims to be up to this Herculean task, as evidenced by his appointment of Mario Ramon Beteta as director general of Pemex. Beteta has sworn that "no immoral deals will be made in the shadow of the largest national industry" while he is director.

But fear of strikes and other disruptions in the crucial oil sector raise doubts that Pemex director Beteta will be able to follow up his tough words on corruption with action. The new director-general has already been criticized for bringing into Pemex well paid but inexperienced associates from the Banco SOMEX, which he previously headed.

Nonetheless, Beteta is smart, hardworking and close to the president. He has helped oust La Quina-backed officers in one small maintenance local and replace them with a slate endorsed by the rank-and-file.

President De la Madrid seems to have determined that taking up the cudgel against malefactors will advance his interests. To pull his nation of 73 million inhabitants from the brink of bankruptcy, he needs all the economic resources at his disposal. That means slicing through the inefficiency, bureaucracy and corruption that holds back the Mexican economy.