Mexico Says U.S. Agents May Carry Guns : Drugs: They also will have diplomatic immunity as part of the two countries’ stepped-up cooperation on anti-narcotics efforts.

The government of Mexico has quietly agreed to allow U.S. drug agents to carry guns while operating in that country and to extend diplomatic immunity to them, Administration officials told The Times on Thursday.

The broadened authority, part of new rules governing the activities of U.S. Drug Enforcement Administration agents in Mexico, signals stepped-up cooperation between the United States and Mexico in anti-narcotics efforts, despite a public dispute over the apprehension of a defendant in the torture-murder of DEA agent Enrique S. Camarena.

The new rules are a surprise because they appear to strengthen the hand of U.S. drug agents in Mexico. Mexico had been expected to move to curtail their operations.

Lack of diplomatic immunity and authority to carry weapons figured in the 1985 slaying of Camarena and has long hindered operations of U.S. drug agents in Mexico, although many have carried arms without written authority from Mexico, officials explained.

Disclosure of the new authority came as a spokesman for Mexican Atty. Gen. Enrique Alvarez del Castillo said that Mexico would assign 49 members of the anti-narcotics units of its federal judicial police to work in the United States. In May, the DEA had 41 agents operating in Mexico, and the total currently is closer to 50, an agency spokesman said.

Robert S. Ross Jr., head of the Justice Department’s international office, said the United States accepted the principle of Mexican drug agents working in the United States.

The Mexican agents will be “working in cooperation with us” to investigate and prosecute “criminal drug trafficking organizations,” Ross said.

An Administration official, who declined to be named, said that the new diplomatic immunity and weapons authority would allow DEA agents to operate more freely and safely in what has long been a restricted environment.

The lack of specific authority to carry firearms was sometimes ignored by DEA agents, often with oral permission of Mexican government officials, an Administration official said. But without written authority to carry arms, the prospect of being arrested by Mexican police without the protection of diplomatic immunity frequently discouraged DEA agents from carrying weapons, even in areas regarded as hostile.

Officials who investigated the Camarena case said he was not carrying a weapon when he was abducted in Guadalajara.

Cornelius Dougherty, a DEA spokesman, declined comment on the new guidelines. He said only that they had been developed by the government of Mexico, which consulted with the United States as a matter of courtesy.

Mexico’s embassy here also would not discuss the new rules.

U.S. drug agents working in Mexico City have enjoyed diplomatic immunity because they operate out of the U.S. Embassy there, but the new rules broaden the coverage to other parts of the country, a DEA official said.

Ross said that he regarded the expanded authority as the latest example of cooperation between the United States and Mexico.

“Sometimes you have a blip,” he said referring to the dispute between Mexico over the apprehension in April of gynecologist Humberto Alvarez Machain.

Wanted for trial in Los Angeles for allegedly administering stimulants to Camarena to permit his continued questioning and torture, Alvarez was abducted by Mexican nationals in Guadalajara in a DEA-approved operation that Mexico contends violated the law. He was flown to El Paso and turned over to DEA agents there.