CARACAS, VENEZUELA -- A historic figure stepped out of Venezuela's political past this week to launch a 100-day campaign aimed at capturing his party's presidential nomination and, he said, rescuing the nation from crisis.

"I feel for Venezuela," declared former president Rafael Caldera, 71, a founder of Venezuelan democracy and of the country's Christian Democratic Party. "I'm ready to face the challenge," Caldera told supporters from Copei, as the party is called.

Caldera's announcement on Wednesday completes the lineup of candidates competing to lead Venezuela's two major parties in next year's presidential race. The bitter nomination battle has divided both parties into warring camps and shaken the foundations of what is now South America's most stable democracy.

Venezuela's political crisis is taking place against the background of economic troubles as Venezuela staggers under a $35 billion foreign debt. Per capita income has dropped 35 percent in nine years and inflation has hit a record annual rate of 40 percent.

The strength of the political system resides in the two parties, which vie peacefully every five years for the spoils of victory at the polls. Never have both parties faced splits at the same time.

When the ruling Accion Democratica (AD) party chooses its candidate in October, and the opposition Copei party selects its contender in November, the two ambitious politicians who lose must step aside gracefully if politics is to proceed as usual.

"Thirty years ago, when democracy began, the political situation was simple: There were clear-cut leaders in each party," said Clemente Cohen, a political columnist and former deputy minister of information in the current government. "Now things are a lot more complicated."

The complications arise from the success of system. Venezuela's democratic tradition began in 1958, long enough for former presidents to be seeking reelection -- as with Caldera, who served from 1969 to 1974, and AD's Carlos Andres Perez, who succeeded him. But powerful party leaders also seek a crack at the job -- Eduardo Fernandez of Copei and Octavio Lepage of AD.

The AD contest has caught the headlines because the center-left party -- with its roots in the labor unions -- currently has an almost absolute monopoly of power. It controls not only the presidency but the judiciary and most municipal governments, and unless AD splits it is likely to defeat Copei next year.

President Jaime Lusinchi has been less concerned with Copei than with preventing Perez from winning AD's nomination. Ex-presidents must be out of office two terms before contesting anew. Lusinchi pushed Lepage, his former interior minister, into the race.

At issue is "control of the party through the end of the century," according to Cohen. Lusinchi wants to pick his successor and establish himself as the heir to deceased party patriarch Romulo Betancourt, who strongly distrusted Perez. Voters were reminded of this when Betancourt's widow was put before the press last month to allege that she had documents proving corruption in Perez's 1974-79 administration.

Perez, 65, is still fondly remembered by poor and working-class voters as the man who doled out millions of petrodollars during Venezuela's oil boom. Lusinchi and his "orthodox" faction regard Perez as an unpredictable populist who ignored party discipline, catered too much to labor and opened government coffers to his cronies.

Although Lusinchi commands the party machinery, Perez holds the hearts of AD's rank-and-file voters. Polls show him with a popularity of more than 50 percent while Lusinchi's candidate, Lepage, has less than 20 percent popularity.

However, parties, not polls, are kingmakers in Venezuela, and Perez must win with the votes of the October nominating convention. The next round of skirmishing will take place on Aug. 28, when AD sets up the system by which is picks its candidates.

Perez wants to increase the number of delegates, but he faces strong opposition from the Lusinchi-Lepage forces. Both sides are talking about the dangers of a split. "It's brinksmanship," said Cohen. "They're playing chicken, and if somebody doesn't swerve, there could be a crash."

AD has divided three times in its history, but Copei has maintained its unity since Caldera and a group of conservative Roman Catholic intellectuals founded the party in 1946.

Caldera sounded the unity theme when he launched his candidacy with a moralistic speech that urged Venezuela to abandon its party in-fighting and take up the cause of "greatness." But Caldera may have to come down off the high road of the elder statesman if he wants to wrest the nomination from Fernandez, whose aggressive campaign has given him a 20 percent lead in the polls.

Youthful and attractive, Fernandez has adopted as his nickname "The Tiger." He wants to be seen as the tough-minded young leader needed for tough times. It remains to be seen if The Tiger will back down for Caldera's last hurrah.