CHICAGO (AP) _ Al Capone's Depression era sin palace - a once opulent hotel that was home to mobsters and madams - is about to become a museum honoring the virtues of women.

The old Lexington Hotel, a one-time brothel and headquarters and home for mobster Capone and his henchmen, will be converted into an international women's museum and research center in time for Chicago's 1992 World's Fair.

The project, developed by the non-profit Sunbow Foundation, a women's organization, will showcase achievements by women around the world in politics, arts, health and science and will honor groups such as the Girl Scouts.

While the museum will be a repository of women's history, it will not ignore the storied past of the Lexington, which had 10 underground tunnels and a dozen secret staircases.

''We're trying to make this into a cultural structure,'' said Patricia Porter, Sunbow's executive director. ''I'm not sure linking Capone to us would be real cool. But we will have something in his honor.''

The 10-story, 400-room Lexington, now vacant, opened in time for the 1893 Columbian Exposition. President Grover Cleveland honeymooned there. Foreign dignitaries and members of high society rubbed shoulders in the lavish ballroom.

But during Prohibition, Capone moved his criminal empire from the Metropole Hotel across the street to the Lexington. And ''Scarface'' was undoubtedly king of his castle.

''He so bullied the owner so he couldn't do much of anything,'' said Ms. Porter, who did extensive research on the hotel. ''He paid something like $18,000 a year to live there.''

From 1928 to 1932 part of the Lexington, decorated with crystal chandeliers and Italian marble, was converted into a brothel, she said.

Capone's personal digs and lavender tub were on the fifth floor.

The South Side hotel still reflects its days of intrigue.

''We found 10 tunnels underground that go in different directions ... and a dozen secret staircases,'' Ms. Porter said. One was behind Capone's medicine chest.

On another floor, a mirror hid a door that led Capone to other buildings where his bookies conducted business.

''We found another room where Capone's bodyguards had shooting galleries,'' bricked up for target practice, Ms. Porter added.

The Lexington tried to clean up its image after World War II, changing its name to the New Michigan Hotel. But the neighborhood deteriorated and the hotel closed in 1980.

It is, however, a national and city landmark, having received the City Council's designation Wednesday. It is a prime example of the Chicago school of architecture with its bay windows and courtyard.

Sunbow, which promotes training and placement of minority women in building trades, purchased the building for $500,000 and, in addition to the museum, plans to use it as a day care center, apartment complex and research center on women's issues. The project will cost $6.5 million.

Renovation will begin March 15, Ms. Porter said, when crews will open a 125-foot-long, 6-foot-wide basement vault ''to see whether there's bodies or money there. I'm bucking for money. We're a non-profit institution.''