ATHENS (Reuters) - Former Greek premier Alexis Tsipras's leftwing Syriza party is leading the conservative opposition by a narrow margin ahead of next month's snap election, two surveys showed on Saturday, suggesting momentum may be shifting towards the opposition.

Tsipras abruptly resigned last week, days after clinching an 86 billion-euro ($97.2 billion) bailout package from European and International Monetary Fund lenders, hoping to crush a rebellion by far-left lawmakers and tighten his grip on power.

The gap between Syriza and the conservative New Democracy party has shrunk to 1.5 percentage points, according to a survey by pollster Alco for Sunday's proto Thema newspaper.

The poll gave Syriza 22.6 percent against 21.1 percent for New Democracy, with 79 percent of respondents saying Tsipras had disappointed their expectations and 66 percent believing he was wrong to call early elections.

"At the start of the race towards the Sept. 20 vote, the game looks open to all outcomes," the paper said. "The collapse of his image in the eyes of the wider public and among those who voted for him enthusiastically just seven months ago resets the political scene."

The poll showed that Popular Unity, a party formed last week by disaffected Syriza rebels who oppose the country's latest 86 billion-euro bailout, would be backed by 4 percent of those polled, enough to enter parliament.

But Syriza's former coalition ally, the right-wing Independent Greeks party would score 2.4 percent, below the 3 percent threshold to win seats in parliament, with undecided voters at 13.6 percent.

Another poll by Kapa Research for Sunday's To Vima newspaper gave Syriza a wider lead - 27.3 percent against 24.2 percent for the conservative opposition - with 57.5 percent expressing a negative view on how his leftist government handled negotiations with the country's international lenders.

"If there are no spectacular upsets during the pre-election period, it seems that Syriza's goal for an outright majority win is unachievable," the paper said.

Story continues

The Popular Unity breakaway party would get 4.8 percent, while the Independent Greeks would barely make it to parliament with 3 percent.

According to this survey, 40.5 percent prefer Tsipras for the office of prime minister against 33.1 percent in favor of New Democracy leader Evangelos Meimarakis.

The poll said 13.2 percent of voters were undecided.

(Reporting by George Georgiopoulos; Editing by Raissa Kasolowsky)