Visiting the world's No. 1 cocaine-producing country, Barry McCaffrey said peace talks to end the nation's 35-year conflict would only work if Colombia's security forces were strengthened against the threat of "narco-guerrillas."
"The United States has paid inadequate attention to a serious and growing emergency," he told reporters after meeting with President Andres Pastrana.
America should provide more battle helicopters and training for Colombian military and police units, he said.
The missing de Havilland RC-7 plane, packed with sophisticated radar and eavesdropping equipment, apparently slammed into an uncharted mountain in bad weather, likely killing the five American soldiers and two Colombian air force officers on board, McCaffrey said. It was reported missing Friday.
The names of the three American officers and two enlisted men based at Fort Bliss, in El Paso, Texas, have not been released.
Low cloud cover and rugged terrain have prevented searchers from reaching the site in southern Putumayo province.
"It's extreme terrain," said Steve Lucas, a spokesman for the Southern Command in Miami. Lucas said specially trained searchers could jump from aircraft, be lowered down by ropes, or hike up to the wreckage lodged high on a mountainside.
The plane dropped off radar screens as it circled over Putumayo, a major drug-cultivation area dominated by the rebel Revolutionary Armed Forces of Colombia, or FARC. It was gathering intelligence on a "routine" counter-narcotics mission, the Army said.
The United States uses satellites, radar installations and overflights to collect data on illegal coca and opium plots and traffickers' movements part of an aid program valued at nearly $300 million this year. Much of the aid has provided crop-dusting planes and the armed helicopters that escort them on fumigation missions.
Despite record spraying, those crops have doubled since 1996, with the most explosive growth coming in areas where the FARC presence has limited operations. The 15,000-member rebel group partly finances itself by taxing drug production and protecting traffickers' laboratories and airstrips.
In Washington last week, McCaffrey proposed major additional U.S. counter-narcotics aid to Colombia and its Andean neighbors. More than a third of the nearly $1 billion package would go to beef up the Colombian army and police so they can conduct anti-narcotics operations in FARC-dominated areas.
His plan also includes aid to the judiciary, and $60 million for programs to wean small farmers off drug crops.
Though American officials insist U.S. aid is for fighting drugs, not rebels, the dividing line is blurring as rebegroups become more involved in drug trafficking.
Peace negotiations begun in January are going slowly, amid doubts about the FARC's sincerity. Hoping to increase pressure on the rebels to negotiate, Pastrana's defense minister recently visited Washington to lobby for an additional $500 million in military aid.