(Adds details of poll, byline)
By Linda Sieg
TOKYO, Feb 15 (Reuters) - Public support for Japanese Prime Minister Taro Aso's cabinet has slumped to 9.7 percent, broadcaster NTV said on Sunday, a level likely to boost calls to replace him ahead of an election that must be held by October.
Aso's support has been sliding after a series of policy flip-flops and gaffes as he struggles with a deepening recession, a divided parliament and a fractious ruling party.
The poll results were the latest bad news for the 68-year-old Aso as he prepares for a visit by U.S. Secretary of State Hillary Clinton from Monday.
Recent surveys suggest the main opposition Democratic Party of Japan (DPJ) stands a good chance of winning the next election for parliament's powerful lower house.
That would end more than 50 years of almost unbroken LDP rule and usher in a government pledged to break the grip bureaucrats have on policy, reduce social gaps that critics say widened because of Koizumi's reforms, and adopt a diplomatic stance more independent of Washington.
Clinton was expected to meet DPJ leader Ichiro Ozawa on Tuesday to sound out his views on the alliance.
The ruling Liberal Democratic Party (LDP) tapped Aso last September in hopes he could lead them to victory at the polls.
Instead, his support has declined sharply, making him wary of calling a snap election.
Aso has repeatedly said his top priority is to rescue the economy from recession, and on Sunday Kyodo news agency reported the government would draft additional steps that could require up to 20 trillion yen ($217.6 billion) in new spending.
RARE REBUKE
Most recently, Aso came under fire for saying he had opposed privatising the postal system, the flagship of reforms pushed by popular Junichiro Koizumi while prime minister from 2001-06.
Postal privatisation was the key issue in the last election for parliament's powerful lower house, when Koizumi led the ruling bloc to a huge victory in 2005.
Aso's remarks prompted a rare and highly public rebuke from Koizumi, fanning speculation that the long-ruling Liberal Democratic Party (LDP) would seek to replace Aso ahead of the election for parliament's powerful lower house.
Asked which parties they would prefer to see gain seats in the next election, almost 52 percent of respondents to the NTV survey backed the DPJ-led opposition, while only 26.2 percent opted for the LDP and its junior coalition partner.
Aso's declining support has been matched by a rise in backing for Ozawa, a former LDP heavyweight who bolted the party in 1993 and helped briefly oust it from power for the only time since the conservative party was founded in 1955.
More than twice as many respondents to the NTV poll -- 40.6 percent -- said Ozawa would be more appropriate than Aso as prime minister, though 43 percent were unimpressed with either.
Aso is Japan's third prime minister since Koizumi stepped down in 2006 after more than five years in office.
Both his predecessors quit abruptly in the face of a deadlock caused by a divided parliament, where the opposition controls the upper house and can delay legislation.
More than 30 percent of respondents to the NTV survey want an election soon, while another 35.8 percent say it should be held after enactment of the state budget for 2009/10 from April.
NTV's survey on Feb 13-15 had 576 respondents. Aso's cabinet support rate was 17.4 in the broadcaster's previous survey in January. (Additional reporting by Yoko Kubota; editing by Andrew Roche)