BERLIN (Reuters) - Support for Germany's opposition Social Democrats (SPD) fell in two new polls out on Friday, and backing for its leading election candidate sank to a record low after he called two top Italian politicians "clowns".

A Politbarometer poll for the public broadcaster ZDF put support for the center-left SPD down 2 percentage points at 28 percent, 13 points behind Chancellor Angela Merkel's conservatives.

A separate Infratest Dimap poll for Germany's other public broadcaster, ARD, suggested support for the SPD had fallen one point to 26 percent. Meanwhile support for the SPD's allies, the Greens, rose to 17 percent, their highest level in 1-1/2 years.

Peer Steinbrueck, the SPD's candidate to take on Merkel in September's election, scored zero on a scale of -5 to +5 in ZDF's survey of Germany's top politicians, his worst score since his candidacy was announced.

Merkel led the survey, with 2.2, followed by her finance minister, Wolfgang Schaeuble, with 1.4.

Steinbrueck's campaign has got off to a bad start. He alienated core supporters by revealing his lucrative earnings as a public speaker, saying chancellors should earn more and scoffing at wine that costs less than 5 euros a bottle.

This week he also caused a diplomatic uproar by calling Italy's former prime minister Silvio Berlusconi and comic-turned-politician Beppe Grillo "clowns" after their strong performance in national elections.

Some 71 percent of those polled felt Steinbrueck's comments, which prompted the visiting Italian president to cancel a dinner with him, were inappropriate. Only 31 percent thought he was the right candidate for the SPD, down from 35 percent in January.

The polls continued to suggest that Merkel's current coalition partners, the pro-business FDP, would fall short of the 5 percent threshold to enter parliament, meaning that she would have to seek a new partner to form a majority.

(Reporting by Sarah Marsh; Editing by Kevin Liffey)