The Oct. 4 election is a key test of the country's ability to consolidate its economic gains after a debt crisis and bailout, which Portugal successfully exited last year. A stable, majority government would be key to maintaining the nascent recovery, analysts say.

The survey by pollsters Eurosondagem, published on the website of weekly Expresso, showed the Socialists slipping 0.5 percentage point to 35.5 percent support and the ruling coalition down 1 percentage point at 34 percent.

Despite their slight lead, the projected results mean the Socialists could take 95 to 101 seats in the 230-seat parliament and the coalition 99 to 102 seats, Expresso said, because of different weightings of electoral mandates across the country.

Friday's poll indicated that a smaller survey published last week, which showed a win for the coalition, was a one-off, and suggested the coalition was losing its recent momentum.

Prime Minister Pedro Passos Coelho is campaigning on his record of having steered the country safely through the debt crisis. The economy is now growing after three years of recession, but the government had to impose harsh austerity and the biggest tax hikes in living memory.

Opposition Socialist leader Antonio Costa has pledged to ease back on austerity and give more disposable income back to households.

The poll was carried out between Sept. 11-16, after Passos Coelho and Costa held their only television debate in the campaign, on Sept. 9. The two also held a radio debate on Thursday, their last duel before the election.

The poll surveyed 1,510 people. The margin of error was 2.52 percentage points.

(Reporting By Axel Bugge; Editing by Andrei Khalip and Larry King)