SÃO PAULO, Brazil — Dilma Rousseff was leading late Sunday in her bid to be Brazil’s first female president, but election officials said she had failed to come up with enough votes to avoid a second round.
With about 98.5 percent of the votes counted, Ms. Rousseff, the former chief of staff of President Luiz Inácio Lula da Silva, had 46.7 percent of the votes to 32.7 percent for her closest rival, the former governor of São Paulo, José Serra. Ms. Rousseff needs to exceed 50 percent of the vote total to win outright.
With Ms. Rousseff coming up short, the election will now be decided with an Oct. 31 runoff. Ms. Rousseff was denied her victory by a strong showing by a third candidate, Marina Silva, the Green Party candidate and a former environmental minister, who captured more than 19 percent.
Analysts expressed little doubt that Ms. Rousseff, 62, would prevail in a second round against Mr. Serra. Despite her lack of political experience and public charm, she has ridden a wave of prosperity and good feeling in Brazil under the leadership of Mr. da Silva, whose approval ratings hover near 80 percent.
After two four-year terms, Mr. da Silva is barred by Brazil’s Constitution from running for a third consecutive term — although he could run again in four years.
If elected, Ms. Rousseff will join a wave of elected female leaders breaking the gender barrier in the past five years, including Michelle Bachelet of Chile, Cristina Fernández de Kirchner of Argentina and Germany’s chancellor, Angela Merkel.
Ms. Rousseff, who was active in armed militant organizations fighting the dictatorship in the 1960s, is considered a competent administrator but is lacking in the kind of seductive charisma that helped make Mr. da Silva so popular. A former union leader with a fourth-grade education, Mr. da Silva’s dirt-poor background resonated with many Brazilians, especially in the northeast and among an emerging lower-middle class he helped create.
Some analysts and foreign investors have expressed concern that Ms. Rousseff’s leftist background could cause her to steer the country left and give the state more control over the economy.
The daughter of a Brazilian mother and a Bulgarian immigrant father, Ms. Rousseff grew up middle class in the Brazilian city of Belo Horizonte.
In an interview last year, Ms. Rousseff denied having participated in an armed action against the government, including the most celebrated incident tied to her, a 1969 armed robbery of the safe of São Paulo’s governor.