MEXICO CITY — Mexico’s top electoral court said it will either declare a president-elect or annul the disputed July 2 race today, ending weeks of uncertainty as to who will replace President Vicente Fox when he steps down December 1.

The court will likely uphold ruling party candidate Felipe Calderon’s slim lead. But the long-awaited ruling — two months, three days, and tens of thousands of pages of legal challenges after voters cast their ballots — was unlikely to end potentially explosive uncertainty or close the country’s growing political divide. Most court rulings so far have favored the conservative Mr. Calderon, who has a 240,000-vote advantage over his leftist rival Andres Manuel Lopez Obrador.

“We are very calm, very sure,” Juan Camilo Mourino, who heads Mr. Calderon’s transition team, said yesterday. “Tomorrow, Felipe Calderon will be president-elect.”

During an early morning session today, the seven magistrates of the Federal Electoral Tribunal will give their final count in the election and decide whether it was valid. While they have the power to annul the election, nothing indicates that they plan to do so. The court’s decision cannot be appealed.

Mr. Lopez Obrador, who stepped down as Mexico City mayor to run for president, already has said he will not accept a ruling against him and is moving forward with plans to establish a parallel government. Mr. Lopez Obrador also plans to convene a national convention of his supporters on September 16 to decide if he should do so.

“The court is going to say, ‘The election was valid, and Calderon is the president, and that’s the end of it,'” a political analyst, Oscar Aguilar, said. “But that won’t turn the page. That won’t end anything.”

For weeks, thousands of Lopez Obrador supporters have blocked Mexico City’s stylish Reforma boulevard and set up a protest camp that has engulfed the capital’s historic central plaza. They say fraud, illicit government spending, and dirty tricks swayed the election in favor of Mr. Calderon, a member of Mr. Fox’s National Action Party. Mexico has a history of electoral fraud.

Mexican presidents are limited by the constitution to a single six-year term, and Mr. Fox leaves office December 1. Protesters say they will not go home until Mr. Lopez Obrador is declared president — and a court ruling in Mr. Calderon’s favor will just fuel their fight.

“The government says everything is peaceful in Mexico,” a 70-year-old retiree who was among those blocking Reforma, Gabriel Juarez, said. “With fraud, there can be no peace.”

Tensions spilled from the streets to the halls of Congress on Friday, when lawmakers from Mr. Lopez Obrador’s Democratic Revolution Party seized the podium of the legislature and blocked Mr. Fox from delivering his final state-of-the-nation address.

An official count gave Mr. Calderon a lead of 244,000 votes — about 0.6% of all ballots cast. Last month, a partial recount overseen by the court’s seven judges reduced Mr. Calderon’s advantage by only 4,000 votes.

Mr. Calderon may appear at the court today in case the judges decided to declare him officially the winner — a ceremony that Democratic Revolution leaders have vowed to block. The party also has pledged to keep Mr. Calderon from being sworn in before Congress on December 1.

A spokesman for Mr. Fox, Ruben Aguilar, said yesterday that “there was no way” protesters could prohibit the presidential handover from taking place. He said the federal government had ways to ensure the president-elect takes office, but he refused to elaborate.