By GINGER THOMPSON
 
MEXICO CITY, Aug. 23 - The Mexican authorities on Monday announced the arrest of Gilberto Higuera Guerrero, who is accused of being a leader of a crime organization responsible for nearly half the cocaine and marijuana entering the United States.

Attorney General Rafael Macedo de la Concha said Mr. Higuera was arrested Sunday in the border city of Mexicali. At a news conference on Monday, Mr. Macedo described Mr. Higuera as a principal operative and hit man in the cartel run by Ismael Zambada. He reportedly was responsible for receiving drug shipments from Tijuana, storing the drugs in Mexicali and supervising their transport to the United States.

The Zambada cartel, authorities said, has seized control of much of the drug trade from Tijuana across the western half of the United States-Mexico border. Mr. Higuera, they said, was responsible for torturing and killing numerous rivals.

Authorities in the United States, where Mr. Higuera is also wanted for conspiracy and money-laundering, had offered a $2 million reward for his capture.

Mr. Higuera, 34, was brought into the drug business by his brother Ismael, a lieutenant in the powerful Tijuana cartel, authorities say. At the time, the cartel was run by two brothers, Ramón and Benjamín Arellano. But in 2000 it began to crumble. First, Ismael Higuera was arrested. Two years later, Ramón Arellano, the cartel's chief assassin, was killed in a shootout with the police. Benjamín Arellano was arrested weeks later. Jesús Blancornelas, a journalist who investigates gangs, said that in the midst of the crisis, Benjamín Arellano sent Gilberto Higuera to Mexicali to help keep the cartel from collapsing. But last year, Mr. Higuera went into hiding. He then abandoned the Tijuana cartel and joined Mr. Zambada. The rift, authorities said, set off waves of violence between the rival cartels.

The arrest of Mr. Higuera on Sunday "solidifies the determination of the U.S. and Mexican governments to finish the job of dismantling the Arellano Félix organization," said Michele Leonhart, deputy administrator of the United States Drug Enforcement Administration.