Álvaro Noboa, a conservative banking and banana magnate, surged ahead by attacking Mr. Correa's admiration for Mr. Chávez and his advocacy of nationalistic economic proposals that seemed inspired by Mr. Chávez's policies. The two candidates are expected to compete in a runoff election on Nov. 26.

"Noboa saw the advantage of running against Correa but also against Chávez," said Simón Cueva, an economist and political analyst at the Corporation for Development Studies, an Ecuadorean research institute.
Mr. Noboa won about 27 percent of the vote and Mr.

Correa 22 percent, with about 70 percent of the votes counted on Monday. Mr. Correa challenged the results and said fraud might have marred the count, which suffered from delays. Election officials suspended a contract with the Brazilian company overseeing electronic tabulations.

Mr. Noboa called Mr. Correa a "friend of terrorists, a friend of Chávez, a friend of Cuba." Mr. Correa said Mr. Noboa would rule Ecuador like a "banana plantation."
It has been a challenging week for Mr. Chávez. Venezuela failed to win enough votes on Monday for a seat on the United Nations Security Council, possibly depriving its president of an international platform he desires.

The unexpected results in the election here, meanwhile, point to growing unease in some parts of Latin America with political projects whose ambitions coincide too closely with those of Mr. Chávez.

"Daniel Ortega must be a little nervous," said Michael Shifter, an analyst at Inter-American Dialogue, a policy institute in Washington. Mr. Ortega, who is considered the front-runner in Nicaragua's presidential election next month, has been endorsed by Mr. Chávez, who has been relatively quiet about Mr. Correa's campaign in Ecuador.

The perception of support from Mr. Chávez has been a mixed blessing in other recent elections. Alan García, whose first term as Peru's president ended in hyperinflation, mounted a comeback this year to defeat Ollanta Humala, an ultranationalist former army officer who had been endorsed by Mr. Chávez.

Venezuela's relations with Mexico remain tense after Felipe Calderón, a conservative, defeated Andrés Manuel López Obrador, a leftist, for the presidency this year. Mr. Calderón used images of Mr. Chávez in television ads during the campaign to criticize Mr. López Obrador.

Now Mr. Noboa, a billionaire who controls more than 100 companies in Ecuador and other countries, signaled that he would end diplomatic relations with Venezuela and Cuba if elected. "I'm not a hypocrite," he said in televised comments. "I don't like the double standard."

Issues other than Venezuela have also dominated Ecuador's presidential race. Mr. Noboa wants to negotiate a trade agreement with Washington and favors extending an agreement that would allow American soldiers to remain in Manta, an air base used by the United States military for drug surveillance flights.

Mr. Correa, like most of the other Ecuadorean presidential candidates, disagreed with Mr. Noboa on those issues. Drawing inspiration from Argentina, Mr. Correa also said he wanted to renegotiate Ecuador's foreign debt, a move that worried foreign banks about dealing with another messy default.

Mr. Noboa and Mr. Correa both campaigned as populists, as did Gilmar Gutiérrez, the brother of a deposed former president, who finished third. Mr. Noboa campaigned from the right as a God-fearing businessman, promising cheap housing and handing out free wheelchairs to handicapped supporters.

Mr. Correa promises a "citizen's revolution" by rewriting Ecuador's Constitution. He also evoked an affinity with Mr. Chávez by professing admiration for the Venezuelan's "Bolivarian" ideals.

Mr. Correa said during the campaign that Mr. Chávez was a friend and acknowledged meeting with him in Venezuela as recently as August. He repeatedly denied receiving campaign financing from Venezuela's government.

Almost until the voting on Sunday, the election seemed Mr. Correa's to lose. One opinion poll by Cedatos/Gallup put his support at 37 percent at the start of October, within grasp of winning the 40 percent necessary for a first-round victory. He would also have needed a 10 percentage point lead to win.