* Bo Xilai's former police chief likely to give evidence against him
* Bo accused of ignoring party hierarchy, acting beyond authority
* Bo trial may start in secret, day earlier than announced
* Bo's son urges fair trial (Recasts, updates throughout)
By Benjamin Kang Lim and Sui-Lee Wee
BEIJING, Aug 20 (Reuters) - One of the charges against disgraced Chinese politician Bo Xilai relates to his flouting the authority of central leaders in Beijing, sources said, an allegation so sensitive that his trial could start one day sooner to hear it in secret.
The charge is abuse of power, and the accusation is that Bo challenged and ignored the will and rules of the ruling Communist Party, the sources said.
Bo is also accused of corruption and taking bribes, but that charge is likely to be heard on Thursday, when the trial is officially scheduled to begin, in a supposedly open session in the court in the eastern city of Jinan.
The scandal surrounding Bo is the most divisive in decades in China and its leaders are keen to swiftly conclude the trial and prevent any ruptures within the Communist Party and society at large.
Many Chinese still support Bo and his populist, left-leaning policies, and ascribe his downfall to ideological differences and not any crime he committed.
The charge of abuse of power involves Bo's former police chief Wang Lijun, who is likely to give evidence against Bo, a source with ties to the leadership and a source familiar with the situation told Reuters.
As police chief of Chongqing, where Bo was party chief until he was dramatically sacked early last year, Wang was known as the strong arm of the law, energetically carrying out Bo's crackdown on crime and gangs.
But he fled to the U.S. consulate in the nearby city of Chengdu in February last year after confronting Bo with evidence that his wife, the glamorous lawyer Gu Kailai, was involved in the murder of British businessman Neil Heywood.
After first helping Gu evade suspicion of poisoning Heywood, Wang hushed up evidence of the murder, according to the official account of Wang's trial. Both Wang and Gu have been jailed for the crime.
When Wang told Bo of his suspicions about Gu, he was "angrily rebuked and had his ears boxed", according to the official account of the incident related by state media.
Bo then sacked Wang, but he did not have the right to do so and thus abused his power, according to the sources.
Wang held a rank equivalent to a cabinet vice minister as he was also a deputy mayor of Chongqing, and it was the prerogative of the Ministry of Public Security and the Communist Party's powerful Organisation Department to appoint or dismiss officials of his rank, not Bo, the sources said.
Bo did not inform authorities in Beijing of Wang's accusations against his wife. Also when the police chief sought asylum in the U.S. consulate, Bo ordered his mayor Huang Qifan and security personnel to besiege the mission and take Wang into custody, the sources said.
"Bo did not report the incident to higher-ups, which he should have done," a source familiar with the case said. "Also, he was in no position to mobilise security personnel to grab someone in another city."
UNCLEAR IF WANG WILL DEPOSE PERSONALLY
Wang spent about 24 hours inside the consulate before being collected by Chinese central government authorities.
It is unclear if Wang himself will appear in court.
"Wang Lijun could testify in court or provide either written or video testimony," a source with ties to the leadership said.
Wang's trial in September last year also began in secret a day earlier than expected because authorities said it involved state secrets.
A court official said he "did not know" if Bo's trial would start on Wednesday, and declined further comment.
But Wang's former lawyer, Wang Yuncai, said it was fairly certain Bo would have to face the court early.
"If it's the abuse of power charges, which involve (state) secrets, then it's highly possible the trial will actually start tomorrow (Wednesday)," said Wang Yuncai.
Bo has not been seen in public since he was fired and placed under investigation early last year, fueling suspicion in China that he will just get a show trial and is the victim of elite infighting.
Bo has agreed to plead guilty to accepting bribes and corruption from his stint working in northeastern China in the 1990s, but will plead not guilty to the abuse of power charge in an apparent bid to show that he is a victim of a power struggle, a source with leadership ties said.
"There are still variables. Bo Xilai may have agreed to plead guilty, but he could turn around, plead not guilty and defend himself," the source said.
Bo's son, Bo Guagua, has urged authorities to grant his father the opportunity to defend himself when he stands trial, the New York Times said on Tuesday.
In a statement to the newspaper, Bo Guagua said he has been denied contact with his parents for the past 18 months.
"I hope that in my father's upcoming trial, he is granted the opportunity to answer his critics and defend himself without constraints of any kind," Guagua said in the statement.
"However, if my well-being has been bartered for my father's acquiescence or my mother's further cooperation, then the verdict will clearly carry no moral weight."
Media reports have suggested that Gu could appear as a witness for the prosecution and may already have provided evidence against Bo.
Two sources familiar with the situation told Reuters on Monday that Gu would only agree to provide evidence against Bo at his trial if a deal had been reached to protect their son.
A deal in which Bo can be swiftly convicted and sent to jail, sparing him a death penalty and with no repercussions for his son, would be in the interest of China's new leadership, sources close to the government say.
Guagua remains in the United States, where he is preparing for his first year at Columbia Law School in New York.
Heywood's family is still seeking compensation for the murder.
The lawyer representing the Heywood family, He Zhengsheng, said that the Heywood and Gu families are narrowing their differences over the compensation claims.
"The gap between the two sides is gradually narrowing," He told Reuters by telephone, without disclosing the figure. (Additional reporting and writing by Ben Blanchard; Editing by Raju Gopalakrishnan)