The poll for public broadcaster RTP showed the Socialists receiving 36-40 percent of Sunday's vote, compared with 25-29 percent for the centre-right opposition Social Democrats.
Three smaller parties also secured parliamentary representation, according to the survey, which gave the more radical socialist Left Bloc 9-12 percent, the Communist/Green coalition 8.5-11.5 percent and the conservative Popular Party 7-10 percent.
Another exit poll by the S.I.C. television channel showed the Socialists winning 36-40 percent and the Social Democrats 27-31 percent.
Both polls said turnout was 57-62 percent of the country's roughly 9.4 million registered voters.
Prime Minister Jose Socrates, the Socialist leader, has pledged big-ticket public works projects to stimulate growth amid forecasts the economy will contract by as much as 4 percent this year. Some 500,000 people - just over 9 percent of the work force - are unemployed.
Socrates has blamed Portugal's economic woes on the global meltdown, and vowed to stick with a modernizing social and economic reform program that has antagonized many, especially trade unions.
The Social Democrats proposed fighting the economic crisis by facilitating private investment. They rejected a stimulus package of state investment, saying public works will saddle future generations with debt.
The Socialists are ready to spend €5 billion ($7.3 billion) on a new Lisbon airport, €3 billion ($4.4 billion) on a bullet train link to Spain and €1.7 billion ($2.5 billion) on a road and rail bridge across the River Tagus at Lisbon.
The Socialist government in the past four years imposed a series of widely contested reforms aimed at boosting the economy in Portugal, which has lagged behind others in the European Union despite receiving billions in EU development aid since joining the bloc in 1986.
The reforms have included raising the civil service retirement age from 60 to 65 and introducing an evaluation system for schoolteachers.
The Socialists are also credited with placing Portugal among the continent's pioneers in the development of clean energy and electric cars, and Socrates has put hundreds of thousands of computers in schools.
Portugal remains western Europe's poorest country, however, with some of the lowest productivity and education levels, and about a third of workers taking home less than €600 (US$880) a month after tax.
The country is shackled by labour laws introduced by radical leftist governments after the 1974 Carnation Revolution ended a four-decade dictatorship.
Social Democrat leader Manuela Ferreira Leite, who was seeking to become Portugal's first elected woman prime minister, also proposed reforms but said they must go deeper and pursue broader consensus.
Before the 2005 Socialist win, Portugal had three governments in three years. Only one minority government has survived its full term since democracy was introduced 33 years ago.
