MEXICO CITY -- (AP) -- Mexico's presidential election this Sunday is widely being
 praised as the fairest and most open in the country's history. It's the result of a
 very long march. And some say there is still a long way to go.

 ``It was an incremental process, a step-by-step process,'' said Roderic Ai Camp,
 a Mexico specialist at Claremont-McKenna College in California.

 Mexico has slowly opened its political system since at least 1946, when
 opposition parties were first allowed into Congress. And it has been slow --
 another 43 years would pass before an opposition governor was allowed to take
 office. Not until 1994 did a candidate outside the Institutional Revolutionary Party
 -- or PRI -- have much chance in a presidential election.

 Even Ernesto Zedillo, who won that year, admitted that while the race was clean,
 ``it was not equitable,'' apparently because of PRI's greater spending, media
 coverage and network of entrenched power.

 There have been at least 11 significant shake-ups of the electoral system since
 1946 as opposition factions gradually leveraged their way to a shot at power.

 Federal officials replaced tough-to-monitor local election organizers in 1946.
 Women won the right to vote in 1953. Proportional representation gave minority
 parties congressional representation in 1963. Minority parties received more rights
 and more proportional seats in 1977.

 Camp said the most important change may be the most recent: the 1996 law that
 removed direct government control over the Federal Electoral Institute that
 organizes the voting.

 That change ``gives it a stronger basis for creating a level of credibility among the
 electorate,'' Camp said.

 After decades of laughable elections, credibility has not come cheaply. The
 Institute -- whose board is dominated by academics -- has a budget of about $860
 million. Some $353 million of that goes to political parties to finance their
 campaigns -- a process meant to end the PRI's financial dominance.

 Critics remain unsatisfied, accusing the government of buying voters or
 threatening to cut their benefits if they buck the PRI.

 ``This is a country whose elections are riddled with fraud, yet not one Mexican
 has gone to jail because of that,'' said Carlos Heredia, spokesman for the leftist
 Democratic Revolution Party.

 ``There is no such thing as a legitimate election in Mexico. When the opposition
 wins it is in spite of the absence of a level playing field, and in spite of the
 prevailing impunity.''

 Mexico has seen other tight presidential races, but none where the result was in
 doubt.

 The first election for the party later known as the PRI was ``the prototypical, the
 dirtiest election,'' said George Grayson, an expert on Mexican elections at the
 Center for Strategic and International Studies in Washington.

 Official results in 1929 showed 1.8 million votes for the party's Pascual Ortiz
 Rubio to 105,655 for Jose Vasconcelos, a quirky educator who was and is
 something of a national hero.

 The result ``was just totally fabricated,'' Camp said.

 Historian Enrique Krauze has written that that Gen. Juan Almazan might have
 won the ``dirty and bloody'' 1940 election over the official candidate, Manuel Avila
 Camacho, had the race been fair.

 As it was, the officials counted just 151,000 votes for Almazan and 2.5 million for
 Avila Camacho. Camp said his investigations indicated Almazan had lost
 nationally -- though he probably carried Mexico City.

 Millions of Mexicans insist that Cuauhtemoc Cardenas won the 1988 election over
 the PRI's Carlos Salinas de Gortari, only to be cheated by fraud.

 Grayson called that race ``a close second'' to 1929 as Mexico's most fraudulent
 election.

 ``Cardenas wasn't ready to fight the system and (incumbent President Miguel) de
 la Madrid wasn't ready to turn over to him,'' he said.

 Cardenas is running again this year for Democratic Revolution.

 Trying to remove the stain of the election, Salinas oversaw major reforms: the
 electoral institute was created with largely independent directors, campaign
 spending was regulated and foreign election observers allowed.

 Some of the most remarkable things about the 2000 race are the things that go
 unremarked: In the past, complaints of ballot stuffing or rigged voter roles were
 common.

 ``It's not an issue anymore, which is a huge achievement,'' Camp said.