The arrest of the brother of former president Carlos Salinas de Gortari in connection with a major political as\sassination has opened a rare win\dow into the inner workings of Mexican politics at its highest and most secretive levels.

Mexicans watched television spellbound late Tuesday as President Ernesto Zedillo's government announced the arrest of Raul Salinas de Gortari and accused him of masterminding the Sept. 28 assassination of Jose Francisco Ruiz Massieu, secretary general of the long-ruling Institutional Revolutionary Party (PRI).

The drama heightened when former president Salinas fought back, going on national television to proclaim his brother's innocence and to launch an unprecedented attack on Zedillo's handling of Mexico's current economic and financial crisis.

Political analysts said there has never been such a drama in the nearly 66 unbroken years of PRI control over Mexico's presidency. A standing rule of Mexican politics is that former presidents do not criticize the performance of their successors and sitting presidents never meddle in the affairs of their predecessors.

On Tuesday, the rule book went out the window.

"Put on your flak jacket. This is war," said a former official in the Salinas government.

"They haven't just broken the rules, they've shattered them. Things will never be the same after this," declared a government insider who has advised presidents in five administrations.

Although Mexicans tend to show a lasting respect for their presidents even after they leave office, Salinas has become the target of widespread resentment because of a public perception that he was responsible for a financial and economic collapse that began Dec. 20, only three weeks after Zedillo became president.

The collapse, which prompted the Clinton administration to authorize an emergency $20 billion package of loan guarantees last week, followed one of the most tumultuous years in Mexican history, one that led to the withdrawal by foreign investors of billions of dollars from the country.

It began with the uprising on Jan. 1, 1994, by peasant rebels in southern Mexico. This was followed by the kidnapping of a billionaire friend of president Salinas, the March 23 assassination of the PRI presidential candidate, Luis Donaldo Colosio, and the later killing of Ruiz Massieu.

Given the fact that Mexico has had nearly seven decades of political stability because of unbroken PRI rule, the combination of so many critical events occurring in a single year struck many, if not most, Mexicans as suspicious. But investigations ordered by Salinas regarding each crisis turned up virtually nothing in terms of clear proof of any conspiracy.

The Colosio killing was written off by Salinas as the work of a lone, crazed gunman. Although evidence of a conspiracy was uncovered in the Ruiz Massieu assassination, the man accused of masterminding it -- PRI legislator Manuel Munoz Rocha -- disappeared.

The chief investigator in the latter case -- the victim's brother, deputy attorney general Mario Ruiz Massieu -- resigned late last year after publicly accusing the Salinas government of protecting the real perpetrators.

When Salinas left office Dec. 1, some people expressed fears that the truth would probably never be made public. Today and Tuesday, however, automobiles and pedestrians paraded past the Salinas mansion in southern Mexico City, honking horns, whistling and shouting insults at the man who won praise from successive U.S. administrations as the economic and political transformer of Mexico.

According to the chief investigator in the case, evidence had begun surfacing months ago that Raul Salinas made payoffs and provided a safe house for Munoz Rocha, the man accused of being the "intellectual co-author" of the Ruiz Massieu assassination. Munoz Rocha remains a fugitive after last being seen in a house allegedly owned by Raul Salinas shortly after the killing.

The federal attorney general's office insists it has been unable to determine a motive for Ruiz Massieu's killing, although separate investigations are underway into a power struggle within the PRI and a dispute involving a major drug cartel.

Ruiz Massieu was among the chief advocates of reform within the PRI at a time a powerful conservative group, nicknamed the "dinosaurs," was attempting to tighten its control of the party. The dinosaurs objected to economic and political reforms engineered by Salinas that meant dismantling the country's system of state management and moving rapidly toward free-market capitalism.

Whether Raul Salinas's alleged participation in the assassination suggests he was aligned with the dinosaurs against his own brother remains a matter of speculation.

The former president's brother was well known across Mexico as the man who managed the Salinas family's substantial fortune during Carlos Salinas's six-year term in office. Like the families of most Mexican presidents, the Salinases reportedly took advantage of their prominent name and web of business connections to amass millions.

Salinas's predecessors or their family members are known to have substantial holdings in Mexican banks, ports, airports and other projects that passed from government ownership to private hands during the 1980s. When Salinas took office in 1988, the privatizations increased to include well over 400 major government enterprises, some of which were purchased by close friends of the president.

For now, the mere fact that Zedillo has lifted Salinas's protection and gone public with the accusation is enthralling enough for a Mexican population accustomed to decades of official silence on any matter having to do with corruption or wrongdoing by the country's leaders.

"This kind of open conflict between presidents has not happened in 60 years," said John Bailey, a Georgetown University specialist on Mexico. "Zedillo is fighting back because Salinas is the one who broke the rules first."

Zedillo authorized Raul Salinas's arrest at a time when political analysts say he is fighting for his own political survival. Zedillo has been heavily criticized, even from within the PRI, for what many observers say is a lackluster performance in the economic crisis, which has led to a stock market crash and a currency devaluation of more than 40 percent.

Bailey said another unwritten rule among Mexican presidents is that the departing leader "cleans the slate" economically for his successor. Last October, according to Zedillo administration officials, the president-elect met Salinas to discuss the state of Mexico's finances and warned that various economic forces were combining to weaken Mexico's currency. Zedillo formally requested that Salinas devalue the peso before leaving office, but Salinas reportedly refused. Three weeks after taking office, Zedillo did it himself, while making references in a speech to financial mismanagement that occurred before he became president.