By Elzio Barreto

SAO PAULO (Reuters) - Ruling party presidential
candidate Dilma Rousseff extended her lead over rival Jose
Serra after taking advantage of free broadcast advertising, a
poll showed Saturday.

Rousseff, President Luiz Inacio Lula da Silva's former
chief of staff, jumped to 47 percent of voters' support from 41
percent last week -- her biggest lead yet in a Datafolha poll.

Serra, former Sao Paulo state governor and health minister,
fell 3 percentage points to 30 percent of voter intention.

The 6-point surge for Rousseff in advance of October's
election was mostly credited to increased exposure after the
presidential candidates took to the airwaves Tuesday with
free television and radio advertising, Datafolha said.

"Serra's campaign seems to have received its death
certificate with the release of the Datafolha poll, which shows
an enormous difference in favor of Dilma Rousseff (from the
Workers' Party)," Folha de S.Paulo newspaper, Brazil's largest
daily, said in an editorial on Saturday.

With recent poll results increasingly showing Rousseff
winning in the first round, she might have a stronger mandate
to push through her legislative agenda.

"It gives greater legitimacy for Dilma," said Cesar
Alexandre Carvalho, a partner at consultancy CAC Consultoria
Politica in Brasilia. "A woman president, coming to power in a
first-round vote, obviously she will have greater bargaining
power. Now, what remains to be seen is what she will do with
that, how it will be used to approve certain projects."

Not even Lula, a former union leader known for his charisma
and off-the-cuff remarks, won in a first-round vote in the 2002
and 2006 elections, suggesting Rousseff could have an easier
time putting together a coalition in Congress.

"TV proves once again its power to reach and penetrate into
the most diverse levels of the Brazilian population, including
those where access to information is scarce," Datafolha
directors Mauro Paulino and Alessandro Janoni said in an
article in Folha de S.Paulo newspaper detailing the poll

The figures followed other poll results during the week
showing Rousseff with more than the 50 percent needed for a
first-round victory if abstentions and blank votes are
excluded, as they are in the election.

Former environment minister Marina Silva garnered 9 percent
of votes in the poll, down from 10 percent in the last survey.

Datafolha polled 2,727 people nationwide on Aug. 20. The
poll has a margin of error of plus or minus 2 percentage
(Reporting by Elzio Barreto; Editing by Bill Trott and Jackie