By Marco Aquino
LIMA (Reuters) - Peru's ruling party gave its backing to presidential candidate Pedro Pablo Kuczynski on Saturday, a day before Peruvians vote in the first round of an election that a left-wing nationalist is favored to win.
Kuczynski, a former Wall Street banker and prime minister, is one of three leading candidates with support from the business community who are vying for a spot in the expected June 5 run-off.
One local pollster said the ruling party's backing boosted Kuczynski's chances for winning second place ahead of right-wing lawmaker Keiko Fujimori and former President Alejandro Toledo.
Left-wing former army office Ollanta Humala heads the polls but he is not expected to secure the 50 percent of the vote needed to avert a second round.
The APRA party of President Alan Garcia, who cannot run again, said Kuczynski had "democratic convictions" that would guarantee the continuation of current government policy.
"Our support is unconditional and we haven't even spoken with (Kuczynski). We've done this with the country's interests in mind," Jorge del Castillo, an APRA figure, told Reuters.
Peru is enjoying a decade-long economic boom and much of the campaign has focused on who can guarantee continued growth, while also spreading the benefits to the one in three Peruvians who still live in poverty.
Despite the strong economic growth seen during his presidency, Garcia has a disapproval rating of about 60 percent and the party is not presenting its own candidate.
Some political analysts say APRA's support could help swing the tight race, though others point to its weakened influence in recent years.
"The backing of APRA could mean about 3 percentage points," said Manuel Saavedra of the CPI pollsters.
"APRA's support is very important, if it wasn't for that it would look tricky for (Kuczynski) to get to the second round," he added.
Kuczynski, 72, a former Wall Street banker who is known as "El Gringo" because of his European parents, is strongly backed by wealthy voters in the capital, Lima. But he could struggle to gain traction further afield.
The most recent polls have shown him gaining ground.
A poll by local survey firm Datum, which was published by Reuters on Friday, showed Humala extending his lead to 31.9 percent of the vote, followed by Fujimori with 22.3 percent.
It gave Kuczynski 17.3 percent and put Toledo, who was the front-runner for much of the campaign, in fourth place with just 15.3 percent.
Humala has surged in the race by shedding his hardline image and recasting himself as a soft leftist in the mold of Brazil's popular former President Luiz Inacio Lula da Silva.
(Additional reporting by Teresa Cespedes; Writing by Helen Popper; Editing by Xavier Briand)