KHARTOUM (Reuters) - Sudanese women's rights activists scuffled with Islamists and riot police on Monday 7 September before a court session for Lubna Hussein, who faces 40 lashes for wearing trousers deemed indecent by the authorites.

Police quickly cleared the scene outside a Khartoum court, beating some protesters with batons and detaining dozens of women supporting Hussein, whose case has attracted world attention since her arrest at a party in July with 12 others.

Hussein's case is being seen as a test of Sudan's Islamic decency regulations, which many women activists say are vague and give individual police officers undue latitute to determine what is acceptable clothing.

A former reporter who was working for the United Nations at the time of her arrest, Hussein has publicised her case, posing in loose trousers for photos and calling for media support.

"Lubna has given us a chance. She is very brave. Thousands of girls have been beaten since the 1990s, but Lubna is the first one not to keep silent," protester Sawsan Hassan el-Showaya told Reuters.

Around 150 protesters, mostly women and including some in trousers, had gathered in a traffic island to wave banners outside the Khartoum court, hemmed in by heavy security and riot police armed with batons and shields.

The women were later joined by dozens of men in traditional Islamic dress who shouted religious slogans and denounced Hussein and her supporters, describing them as prostitutes and demanding a harsh punishment for Hussein.

Scuffles erupted, and one bearded protester grabbed a paper banner and ripped it to pieces. Riot police with batons moved in, beating back protesters. They later loaded dozens of women into a van and drove off.

"They are beating us. They are trying to provoke us into violent action so they can react and clear us off the streets ... I never thought this would happen," Nahed Goubia, a surgeon in a white trouser suit, said before riot police cleared the area.

Defence lawyer Nabil Adib Abdalla has previously said the law on indecent dress was so wide it contravened Hussein's right to a fair trial. Hussein is challenging the charges, arguing her clothes were respectable and so she did not break the law.

Ten of the other women arrested with Hussein have pleaded guilty and have been whipped, Hussein previously said.

The judge had adjourned Hussein's last court session to investigate whether she was immune from prosecution because she was working as a press officer for the United Nations at the time of her arrest.

Hussein has said she resigned from her U.N. job to give up any legal immunity so she can continue with the case, prove her innocence and challenge the decency law.

U.N. officials have said the United Nations told Sudan that Hussein was immune from legal proceedings as she was a U.N. employee at the time of her arrest.