BERLIN (Reuters) - Germany's opposition Social Democrats (SPD) and Greens have gained momentum after winning a regional vote last week, a poll showed on Wednesday, giving them a much-needed boost in their bid to oust Chancellor Angela Merkel in September's election.
The Forsa poll put the SPD up two points at 25 percent and the Greens up 1 point at 15 percent. Merkel's conservatives dropped 2 points but are still the biggest force at 40 percent.
However, her Free Democrat (FDP) coalition partners were flat at 4 percent, one point below the threshold needed to enter parliament.
The SPD has been buoyed by a victory in the state of Lower Saxony on January 20 where they and their Greens allies ousted the centre-right coalition from power in a vote widely viewed as a barometer of public sentiment before the national election.
The win came despite a botched start to the SPD's national campaign from Peer Steinbrueck, their candidate to challenge Merkel for the chancellorship.
The former finance minister has alienated many core SPD supporters by revealing he raked in over 1 million euros (859,000 pounds) for speeches in the last three years, saying chancellors should earn more and scoffing at wine that cost less than 5 euros a bottle.
However, the Forsa poll showed that the SPD and Greens do not have enough combined support to oust Merkel's conservatives. Such an outcome in the September election could result in a "grand coalition" of conservatives and SPD, repeating the formula of Merkel's first government from 2005 to 2009.
Merkel, riding high in her personal ratings, will meet the heads of her coalition parties on Thursday in an effort to fend off criticism that her government has run out steam. However, few big policy decisions are expected.
A strong result in Lower Saxony for the FDP has not helped the party nationally, the poll showed. The conservative leader in Lower Saxony, fearing he would lose his coalition partner, had encouraged his supporters to vote for the FDP, a tactic which backfired badly as too many followed his advice.
"The traditional FDP voter base has not grown as a result of this," said Forsa chief Manfred Guellner, adding, however, that there was potential for a liberal party in Germany.
"More than 30 percent of citizens can imagine voting for a liberal party. But not the existing one with its unpopular leader," said the pollster.
Reporting by Madeline Chambers; Editing by Stephen Brown