KUALA LUMPUR, March 3 (AFP) - 15:39 - A key witness against ousted Malaysian deputy premier Anwar Ibrahim lied when she claimed that Anwar had fathered her sister-in-law's child, the appeal court was told Friday.

On the fifth day of his appeal against a corruption conviction and six-year jail term, Anwar's lawyers sought to destroy the credibility of Ummi Hafilda Mohamad Ali, the sister of his former political secretary.

Ummi Hafilda set the whole affair in motion when she and Azizan Abu Bakar, then-driver for Anwar's wife, wrote to Prime Minister Mahathir Mohamad in August 1997 making allegations of homosexual and heterosexual misconduct against Anwar.

Last April Anwar was convicted of corruption -- using his official powers to cover up those allegations.

He is separately on trial for sodomising Azizan, a crime punishable by up to 20 years, but that trial is adjourned till the corruption appeal ends.

Lawyer Gurbachan Singh said Ummi's allegations that Anwar was the father of her sister-in-law's child had been proved untrue and this showed she was capable of making false allegations.

He said Ummi also lied when she claimed she had not met Khairuddin Hassan, the publisher of a book entitled "50 reasons why Anwar cannot become Prime Minister," between July and November 1998.

"She is lying, she and Khairuddin met and wrote a letter to Anwar in September that year," he said.

The letter, read out by Gurbachan, attacked Anwar using derogatory language.

Gurbachan said the language in the letter should have alerted the trial judge, Augustine Paul, that Ummi had ulterior motives.

He also asked the judges to dismiss the prosecution case that police acting on Anwar's orders forced Ummi and Azizan to retract their allegations of sexual misconduct.

"They consulted lawyers before their arrest but after their release they did not lodge any police report or complain ... it is inevitable Ummi and Azizan gave voluntary statements," Gurbachan said.

He said Ummi and Azizan were not under arrest when they gave statements apologising for making the allegations against Anwar.

"Therefore the prosecution stand that they were induced, threatened or forced into giving the (retraction) statements cannot hold water," he said.Gurbachan urged the court to accept Anwar's testimony that there was a second report on investigations into the sexual allegations, which was sent to Mahathir.

He said the report named Mahathir's then-political secretary Aziz Shamsuddin, Rahim Thamby Chik (an ex-chief minister of Melaka state) and Megat Junid Megat Ayob (then a minister) as people who wanted to exploit the sexual allegations.

Anwar, 52, was sacked by Mahathir on September 2, 1998. He was detained 18 days later, initially under an act allowing detention without trial, after leading mass anti-government protests.

He says he is the victim of a high-level political conspiracy.The appeal was adjourned till Monday.

"It will be the longest appeal in the country's history...the sodomy trial will be postponed until the appeal hearing is over," another of Anwar's lawyers, Christopher Fernando, told reporters.

"We expect to conclude our case by Wednesday or Thursday," Fernando said. Prosecution sources said they may take a week to present their arguements.The judge in the sodomy trial was originally due to hear arguments next Monday on whether Mahathir should be called by the defence to testify.Fernando said they had asked for more time to file affidavits to show what evidence they wanted from Mahathir.