UPDATE 4-Unpopular Japan PM's job at risk after Tokyo vote

For more stories on Japanese politics click [ID:nPOLJP]

* Japan ruling bloc suffers big defeat in Tokyo election

* PM job at risk, ruling party chaos seen

* Poll portends big ruling bloc defeat in national vote (Recasts with ruling bloc losing majority in Tokyo election)

By Linda Sieg and Isabel Reynolds

TOKYO, July 12 (Reuters) - Unpopular Japanese Prime Minister Taro Aso's job is at risk after his ruling bloc suffered a big defeat in a Tokyo poll on Sunday, with critics in his party now expected to intensify moves to ditch him before a national vote.

NHK public TV said Aso's Liberal Democratic Party (LDP) and its junior partner had lost their majority in the Tokyo assembly while the opposition Democratic Party won the most seats in the vote, which is considered a barometer for the national election.

Aso has been thought to be eyeing an early August national vote, but many in the LDP were already opposed to a move they fear would be political suicide.

NHK public TV said Chief Cabinet Secretary Takeo Kawamura and LDP Secretary General Hiroyuki Hosoda agreed in talks on Sunday the outcome of the Tokyo vote would not affect national politics and Aso would not be blamed for a defeat.

However, Kyodo quoted another unidentified ruling party executive as saying: "This is a great blow against the Aso government."

The long-ruling LDP has been wracked by internal dissension of late, with Aso critics openly urging an early party leadership vote to replace him while his allies defend his right to call a general election at a time of his own choosing.

"There will be confusion inside the LDP. People will try to oust Aso and he will try to stay on," said Keio University political science professor Yasunori Sone.

"It is not clear if they can oust him and if they did, would support for the LDP increase? Not much," Sone said. "Chances the LDP could win under a new leader are very small. That has become clearer as a result of this Tokyo election."

NEARLY UNBROKEN RULE

A Democratic Party victory in the lower house election would end half a century of nearly unbroken rule by the business-friendly LDP and raise the chances of resolving a deadlock in a divided parliament as Japan tries to recover from its worst recession since World War Two. [ID:nECONJP]