(Adds regional data in paragraph 13)
By Hugh Bronstein
BOGOTA, June 18 (Reuters) - Colombian cocaine production edged down last year despite an increase in crops used to make the drug, showing that law enforcement efforts have reduced the efficiency of the business, the United Nations said on Wednesday.
U.N. investigators said the output in the world biggest cocaine-producing country was 600 tonnes in 2007, down 2 percent from the year before.
Planting of coca bushes used to make cocaine meanwhile rose to 99,000 hectares in 2007, up 27 percent from 2006.
Farmers are quickly replanting in more remote areas after the government sprays herbicides on their coca fields, part of a multibillion-dollar U.S.-backed program. A record 538,700 acres (218,000 hectares) of coca were eradicated last year.
"What’s happening is that the efficiency of production is going down," said Aldo Lale-Demoz, representative in Colombia for the U.N. Office on Drugs and Crime.
"After each eradication, farmers immediately replant somewhere else," he said. "That takes time. They go further inside forests. They go further afield from their homes. They will not tend those plots as well as they did before, so the productivity of those secondary lots is much lower."
Productivity increased in 2003 through 2005, according to U.N. figures, as traffickers responded to the spraying by looking for ways to produce more cocaine per hectare of coca.
"If efficiency moved down last year it was only after several years of it moving up," said John Walsh, an analyst with the Washington Office on Latin America.
"Unfortunately, net production of cocaine in Colombia remains stable and high."
Colombian police say they are cracking down on access to chemicals used to make cocaine in secret jungle laboratories, another factor reducing production efficiency.
Crime is down in this Andean country under President Alvaro Uribe, a White House ally who was re-elected by a landslide in 2006 and remains popular in part for spurring economic growth.
The U.N. report nonetheless calls the sharp increase in coca cultivation "a serious and worrisome reversal" of previous declines in areas covered by the illegal crops.
The United Nations had reported a drop from 166,000 hectares of Colombian coca cultivation in 2000 to about half that amount in 2006.
Cocaine output in the Andean region, including Peru and Bolivia, rose 1 percent last year to 994 tonnes. Bolivian production alone shot 11 percent higher to 104 tonnes while coca cultivation regionwide rose 16 percent to 181,600 hectares, the U.N. report said. (Editing by Todd Eastham)