By Alexandra Alper and Zach Dyer SAN JOSE, Feb 2 (Reuters) - Costa Rica's centrist ruling party candidate Johnny Araya took a slight early lead in Sunday's presidential election and was on course to face a tough run-off after a strong showing by two leftist parties, partial results showed. Araya, a former mayor of the capital San Jose, had around 30.6 percent support with votes in from 50.3 percent of polling booths, while leftist newcomer Luis Guillermo Solis was in second place with around 29.4 percent. Left-wing lawmaker Jose Maria Villalta was third with 17.4 percent. An April run-off between the top two vote-getters is required if no single candidate wins more than 40 percent of the vote on Sunday. Araya could face the prospect of a consolidated left-wing vote in the run-off, which could spell defeat for his ruling National Liberation Party. Araya, 56, has promised to reduce poverty and has sought to distance himself from President Laura Chinchilla's scandal-plagued government while painting rivals as radicals. Araya on Sunday proclaimed his candidacy "the safest, most responsible option" for Central America's second-largest economy. But voter anger over government corruption buoyed a challenge from his left-leaning rivals, who also promised to tackle inequality in the coffee-producing nation. Gaffes, such as underestimating the price of milk in an interview, distanced Araya from some voters. A prosecutor's probe into allegations of abuse of authority and embezzlement while Araya was mayor of San Jose have also dampened his appeal. Solis, who cut his teeth working in Costa Rica's foreign ministry, has appealed to voters by pledging to improve infrastructure, overhaul the country's universal health care provider and stamp out corruption. That resonated with some voters after Chinchilla sparked outrage by accepting flights on a private jet, despite laws barring public officials from accepting sizeable gifts. Solis nudged ahead of Villalta after trailing in polls before the vote. But some see Araya as the more moderate option. "There are two extremes, the extreme right ... and communism. We favor the center and that's the best option for Costa Rica," said David Perez, 21, who works for a family-owned business. The eventual winner will have to tackle growing government debt that totals more than half of gross domestic product. "If they don't do something, then this somewhat negative trend on the debt could continue and that could have an impact on the credit rating," said Joydeep Mukherji, a sovereign credit analyst with Standard & Poor's, which rates Costa Rica at BB with a stable outlook. Araya has vowed to tackle the deficit by limiting public sector bonuses, creating a capital gains tax and shifting to a value-added tax.