KUALA LUMPUR, Sept 21 (AFP) - Malaysian opposition leader Lim Kit Siang on Monday denounced the arrest of ousted deputy premier Anwar Ibrahim as ''most deplorable'' and said his detention proved the government had no strong case.

Lim, head of the opposition Democratic Action Party, said the arrest marked a ''great test of public confidence in the system of justice in Malaysia'' and questioned the timing of the action with Britain's Queen Elizabeth in town.

''The manner of the arrest is most deplorable -- why was it necessary for a police special unit to storm Anwar's house to arrest him when Anwar's lawyers had already written to police expressing Anwar's full preparedness to cooperate?'' he asked.

The opposition leader also noted that Anwar was detained under the draconian Internal Security Act (ISA), providing for indefinite detention without trial.

''Detention of Anwar under ISA can only mean that the government has no strong case,'' he said, referring to the ''multitude of serious allegations of sexual misconduct, corruption, sedition and treason'' against him.

Lim added that the use of the ISA ''reinforces Anwar's allegation of a high-level political conpiracy to topple him.''

The opposition party called for Anwar to be ''produced and charged in court or he should be released immediately.''

Lim also questioned the timing of the move only a day before the end of the Commonwealth Games, which Malaysia has been hosting since September 10.

''The question is why the arrest of Anwar could not be put off another 24 hours so that the Commonwealth Games could be completed without any hitch or blemish,'' the opposition leader said.

Lim suggested one factor might have been Anwar's open challenge to Prime Minister Mahathir Mohamad to resign, which found ''resounding response'' from the tens of thousands of people who attended an Anwar rally Sunday.

Other possible factors were that many people do not believe the charges of sexual impropriety against Anwar, Lim said. They were also ''sceptical'' about the sudden admissions of two Anwar associates who were sentenced to six months in prison Saturday for reportedly having sex with the finance mninister.