The Baldies have battled the Gulf Cartel in shootouts in the beach resort of Acapulco that have horrified residents and tourists in recent years.
Beltran Leyva and three other people arrested with him were carrying some $US900,000 - about $A1 million - in cash in two suitcases. "Among his key functions was transporting drugs, money laundering, and bribing officials," the spokeswoman said yesterday.
Prosecutors say Beltran Leyva is a close lieutenant of Joaquin "Shorty" Guzman, Mexico's most wanted man and the head of an alliance of smugglers based in Sinaloa state.
The United States, whose Congress is debating sending surveillance and detection equipment to help Mexico's year-old drug crackdown, praised the arrest, with Ambassador Tony Garza in Mexico calling it a "significant victory".
The Sinaloa gang is in a bitter fight with the rival Gulf Cartel, based south of Texas, for control of smuggling routes.
More than 2500 people died in gangland-style killings last year as Mr Calderon launched an army crackdown on drug cartels. Many of the killings were gruesome, with victims often tortured or beheaded and their bodies left in the street.
Beltran Leyva, who has four brothers also accused of being leading traffickers, was the head of two teams of hitmen known as "The Baldies" and "The Blondies" in two western states.
Mr Calderon has deployed 25,000 troops and federal police to crush drug cartels in an offensive that has had mixed results. Scores of traffickers have been arrested, and some extradited to the US, but violence has not abated.
Drug hitmen last week broke traditional codes of honour against killing children when they murdered a three-year-old boy and a girl aged nine in the tough border city of Tijuana.
US Attorney General Michael Mukasey said on a visit to Mexico last week that the spurt in killings emphasised the need to keep up pressure on "drug terrorists" and pledged tighter controls on US guns flowing across the border illegally.