The disappearance of a U.S. reconnaissance plane in the remote and guerrilla-controlled hills of southern Colombia has underscored the risks involved in American efforts to fight drug trafficking here by expanding aid to the Colombian police and military.

Retired Gen. Barry R. McCaffrey, director of the Clinton administration's Office of National Drug Control Policy, spoke in support of U.S. efforts in discussions here Monday and today with Colombian officials on what he called a "serious and growing emergency in the region." After two days of talks, scheduled before the U.S. plane went down, he left Colombia to hold similar meetings in Ecuador, Venezuela and Curacao.

McCaffrey's visit came amid concern in Colombia and elsewhere in Latin America that escalating guerrilla violence combined with the drug threat may prompt the United States to expand its military role in this Andean nation of 37 million people. These concerns have multiplied particularly because the line has blurred between the illegal drug trade and activities of Marxist guerrillas, who reap huge profits by protecting growers of illicit crops and extorting money from them.

McCaffrey said U.S. military intervention is not in the offing, but American assistance will continue in the form of training, supply, intelligence sharing and alternative economic development in drug crop regions. "The United States has paid inadequate attention to a serious and growing emergency in the region," he declared. "And this is a problem we have to face in the coming 10 years; this is not a problem of the next 18 months."

The United States is providing $256 million this year in anti-drug assistance to Colombia, the third-largest recipient of American military aid after Israel and Egypt. Earlier this month, McCaffrey recommended that $1 billion in "emergency drug supplemental assistance" be made available promptly to Colombia and other nations in the Andes and the Caribbean region that are cooperating with the United States in the fight against international drug trafficking.

Airborne efforts to reach and identify wreckage spotted on a mountainside in Putumayo province, believed to be that of the missing De Havilland RC-7 reconnaissance plane, were hampered for a third straight day by clouds and dense fog that typically shroud the jungle terrain near the border with Ecuador. A defense ministry source said late today that soldiers and rescue workers were approaching the crash site on foot from several nearby towns but were not expected to reach the wreckage until early Wednesday.

The aircraft and its crew of five U.S. Army soldiers and two Colombian air force officers dropped out of sight Friday while on a drug surveillance mission that Colombian authorities say apparently ended with a crash into an uncharted peak at an altitude of 7,000 feet. Attempts to fly investigators to the site have been complicated by the fact that the territory is controlled by guerrillas of the Revolutionary Armed Forces of Colombia, who fiercely oppose U.S. anti-drug aid to Colombia. The insurgents, who have kidnapped U.S. citizens and in March killed three American indigenous-rights activists, routinely shoot at low-flying crop dusting planes that are trying to eradicate fields planted with illegal coca -- the raw material of cocaine.

Military officials said there is no evidence to suggest that the RC-7, which was carrying infrared sensors and electronic systems capable of eavesdropping on ground communications, was fired on by the guerrillas or that there are rebel forces near the wreckage. But the crew is believed to have been killed in the crash, which would make them the first U.S. troops to die in Colombia's U.S.-supported drug war.

"There is no reason to believe anybody is alive," McCaffrey said while visiting a Colombian military base in Tres Esquinas, where U.S. advisers are helping train a new 1,500-member anti-drug battalion.

When it disappeared, the plane was on a routine anti-drug support flight. Last year, U.S. authorities undertook more than 2,000 such flights throughout the region, originating from Florida, Puerto Rico, Ecuador and the Caribbean island of Curacao. The missions were carried out with "absolute deference to national sovereignty when entering the airspace of one of our hemispheric partners," McCaffrey said.

While the crash of the plane has captured official attention for the present, the deteriorating security situation in Colombia -- where rebels control about 40 percent of the countryside -- and a continued increase in coca and opium poppy cultivation will likely shape the debate over levels of future anti-drug assistance.

"The international drug control gains that we have achieved over the last three years are now eroding," McCaffrey wrote in a July 13 discussion paper for Secretary of State Madeleine K. Albright. "Traffickers have established new routes to evade the regional interdiction effort and are expanding cultivation and production."

In the case of Colombia, which supplies about 80 percent of the world's cocaine, he noted that coca cultivation has doubled in three years from 150,000 acres in 1995 to 250,000 acres in 1998. Over the last decade, poppy cultivation also has expanded, from almost none to more than 15,000 acres, producing enough high purity heroin to meet more than half the U.S. demand.

Said one senior congressional aide who specializes in anti-drug issues: "The policy debate now undoubtedly becomes more intense, as to whether to get more assets down there of the kind that should have been there four or five years ago as things intensified."