A paramilitary army that fights Colombia's leftist guerrillas on the same side as the U.S.-backed military has agreed to a two-month cease-fire and promised to stop trafficking in drugs in hopes of starting formal peace talks with the government early next year, officials said today.

The temporary truce, after two months of talks with Roman Catholic bishops, was offered despite deep divisions within the United Self-Defense Forces of Colombia, or AUC, as the 15,000-member federation of regional paramilitary groups is known, over political strategy and lucrative ties to drug smuggling.

Terms of the cease-fire, scheduled to begin Sunday, have not been spelled out pending an official announcement, officials said. But based on past practice, they added, the AUC will likely suspend offensive military operations, but not self-defense. As part of the cease-fire, AUC leaders also have pledged to stop participating in the drug trade, which generates most of its financing and has prompted the indictment in the United States of its top leaders, Carlos Castano and Salvatore Mancuso.

Since his election earlier this year, President Alvaro Uribe has insisted that formal talks with guerrilla or paramilitary groups would first depend on a cease-fire. There have been no signs so far that the guerrillas are ready for a truce. In the meantime, Uribe has vowed that the army will pursue the war against the guerrillas with increased energy and has sought more U.S. aid to enable it to do so.

Uribe's approach toward ending Colombia's 38-year civil war differs significantly from that of Andres Pastrana, his predecessor. Pastrana conducted a fruitless three-year negotiating process with the Revolutionary Armed Forces of Colombia, or FARC, as the 18,000-member Marxist-oriented insurgency is known, without a nationwide cease-fire. Those talks never received support from the United States, which has been aiding Colombia with a $1.3 billion package devoted mostly to military equipment and training.

Pastrana had also turned over a 16,000-square-mile swath of southern Colombia to the FARC in return for the guerrillas' participation in the peace talks.

Uribe has offered no such incentives, but his peace commissioner has been trying to set up talks with the FARC that could lead to an exchange of guerrilla prisoners for politicians the group has kidnapped. So far, U.S. officials have expressed support for Uribe's early overtures to the AUC, the FARC and the National Liberation Army, or ELN, as the smaller guerrilla group is known. All of them appear on the State Department list of foreign terrorist organizations.