SANTIAGO, Chile (AP) _ Heavy fog hampered the search today for a plane that disappeared with five people aboard, including two U.S. Food and Drug Administration officials who were inspecting Chile's agricultural exports.

The search for the two-engine Cessna 206 began at 8 a.m. near Copiapo, the desert city 500 miles north of Santiago where the plane took off Wednesday.

The aircraft was scheduled to arrive in Santiago on Wednesday night.

Heavy fog and cloudy skies grounded some search planes during the morning, but weather conditions cleared later and the operation resumed at full strength, an official at the Copiapo airport said in a telephone interview.

A day-long search Thursday, involving at least 21 planes and helicopters and land patrols, turned up no sign of the plane.

Authorities have said there was no indication of sabotage and that no guerrillas are believed to operate in the areas the plane was to fly over.

The Americans - FDA officials John Harty Jr. of Silver Spring, Md., and Patrick Pouzar of Nashville, Tenn. - arrived in Chile on Saturday.

They were checking security procedures in the harvesting, packing and transport of Chilean fruits being exported to the United States.

Last year, two grapes laced with cyanide were found in Philadelphia in a shipment of fruit from Chile. The finding prompted a temporary suspension of the sale of all Chilean fruits in the United States.

The Chileans aboard the missing plane are Oscar Badilla, a government agricultural official; Sergio Lazcano, an executive of the Fruit Exporters Association; and an unidentified pilot, police officer German Fuentes said.

Police said the search was covering the 500-mile-long route between Santiago and Copiapo. But rescue workers were concentrating on the Copiapo area because the Cessna's last radio contact occurred only 15 minutes after it took off from that city at 5:10 p.m. Wednesday.