Mexican and U.S. authorities searching for scores of bodies that may be buried on the outskirts Ciudad Juarez, Mexico, said yesterday they found what could be human remains at one of four desolate sites where the investigation is focused.

A U.S. official familiar with the search, meanwhile, said an unspecified number of informants for U.S. law enforcement agencies may be among the more than 100 suspected victims of drug-related violence who have disappeared from the U.S.-Mexico border region near El Paso in recent years and may be among those possibly buried at the sites.

The El Paso-Juarez area has long been described by authorities as a multibillion-dollar conduit for Colombian cocaine flowing into the United States, a corridor run by a cartel reputedly headed by a Mexican drug lord, Amado Carrillo Fuentes, before his death in 1997. According to an association of families of people who have disappeared, at least 196 people, including some Americans, have vanished in the region since the early 1990s, many of them informants and low-level associates of the cartel.

On Monday, dozens of Mexican federal police and FBI agents descended on two ranches on the desolate outskirts of Ciudad Juarez in a search for bodies that expanded to include four sites in the area, said Jose Larrieta Carrasco, the head of the organized crime unit in the Mexican attorney general's office.

Speaking to reporters in El Paso, Larrieta Carrasco provided only sketchy details on the find, saying that investigators had turned up "some remains that could be human remains." He said he could not estimate the number of bodies that may be buried at the four sites.

He also declined to say specifically what led authorities to the sites. "We have very concrete information as to these sites, and we did use technical equipment to locate these sites, and we're still working," he said.

"We are in the process of investigating," he said. "The work continues at an accelerated rate. . . . What I could point out is, we have information in Mexico that could lead to bodies of people who have disappeared."

The discovery comes as U.S. authorities say increased amounts of marijuana and other drugs have been flowing across the Mexican border into the United States. FBI Deputy Director Thomas J. Pickard said the joint drug-related probe is taking place in the U.S. and in Mexico.

U.S. officials who declined to be identified said the probe was aided by a former Mexican police officer who played a role in the suspected killings and who provided critical information to the FBI that led to sites.

In Washington, Pickard said there had been an amassing of shared intelligence by the FBI and Mexican authorities over a period of months that led to the searches of the four sites.

"We have developed information from a number of different sources," Pickard said. "The FBI developed information, the Mexican authorities developed information, and we brought that information together, and we have the results we have right now. We are still trying to develop further information."

As for who may be buried at the sites, a U.S. official who asked not to be identified said, "The speculation still is that there are a number of victims related to drug trafficking, some of which are suspected of being informants" for the Drug Enforcement Administration, the U.S. Customs Service and the FBI.

"Most of the information we have to date shows these individuals were buried there at least two to three years ago," Pickard said. "We believe these individuals were killed for their knowledge of, or participation [in], or being witnesses to, certain drug endeavors." Of the Americans possibly buried at the sites, "first and foremost, we want to find the remains and bring them back to the families," Pickard said.

Pickard said Mexican officials have detained some people who lived on or around the ranches where the searches are being conducted and noted that contrary to some media reports, no U.S. law enforcement officials are missing or believed to be buried there.

On Monday, Mexican officials said that 22 of the bodies that could be buried at the sites are Americans. But speaking to reporters yesterday, President Clinton said he had received no confirmation that 22 of the victims were Americans.

Clinton called the suspected graves a "horrible example" of the excesses of Mexican drug cartels. "It reinforces the imperative of our trying not only to protect our border but to work with the Mexican authorities," he said.

In addition to digging at the sites, Pickard said the FBI would be using "ground-piercing radar" to search for remains. He said the FBI had entered Mexico to assist in the effort at the request of government officials there.

Duggan reported from El Paso; Vise from Washington. Staff writer Lorraine Adams in Washington and correspondent Molly Moore in Ciudad Juarez contributed to this report.