The National Action Party, which has held the job since 1989, when it became the first party to defeat the Institutional Revolutionary Party in an election, was ahead by a few percentage points after polls closed Sunday night, officials said.

But then, with about 97% of preliminary results tallied in a quick count by a private contractor, officials suddenly halted the count and said results would not be available until Wednesday. The officials cited a problem with algorithms.

Some Mexicans smelled a rat.

They recalled the notorious presidential election of 1988, when leftist candidate Cuauhtemoc Cardenas appeared to be defeating Carlos Salinas de Gortari of the Institutional Revolutionary Party, or PRI. At a certain point, the system conducting the ballot count had what authorities at the time claimed to be a mechanical failure. When the computers came back up, Salinas was declared the victor.

"Once again, we are going back to the story of the 'failing system,' " said Jesus Zambrano, national head of the leftist Democratic Revolution Party, or PRD. His party was running in a coalition with the National Action Party in Baja. "Why can't the PRI just accept defeat?"

Gustavo Madero, leader of the National Action Party, or PAN, said the elections Sunday, which were marred by violence and corruption scandals, represented a throwback to the era when the PRI used electoral fraud and graft to hold on to power for seven decades.

Madero said he would reassess whether his party would continue to cooperate with President Enrique Peña Nieto's efforts to push forward numerous reforms aimed at boosting the economy. An especially critical overhaul of the giant state oil-and-gas company is up next. Peña Nieto, who last year won the presidency back for the PRI after 12 years of PAN rule, has staked much of his government's success on the reform but will not be able to get it approved without the PAN's help.

The PAN's candidate in Baja, Francisco Vega de Lamadrid, said Monday that he remained confident of victory, citing the now-canceled count that gave him 47% of the vote over 44% for the PRI's Fernando Castro Trenti.

Top PRI officials brushed aside the complaints. Peña Nieto called on parties to respect the results and vowed to continue "dialogue and accords" with all political forces.

Mexicans on Sunday voted for hundreds of local and regional posts in 15 states. The PRI won the mayorships of eight of 13 state capitals that were up for grabs. The PAN, either alone or in coalition with the PRD, won the rest. The PRI also took City Hall from the PRD in Cancun. The results for state legislatures were still being counted.

The PAN was keen to hold on to Baja as a way to stanch the rapid decline of the conservative party, reeling from internal fighting and scandals as well as the loss of last year's presidential race. The PRI wanted to take back Baja for symbolic reasons, given that it was the first state it lost and also to further consolidate its power nationwide.

wilkinson@latimes.com

Cecilia Sanchez of The Times' Mexico City bureau contributed to this report.