Lawmakers voted to pull Bolivia out of a U.N. drug convention because the world body refuses to decriminalize the chewing of coca leaf, the plant that is also the raw material for cocaine production.

The government-controlled lower house, acting at President Evo Morales' request, passed a bill Wednesday that would remove Bolivia from the 1961 United Nations Single Convention on Narcotic Drugs after reading a petition from Morales and hearing arguments from Foreign Minister David Choquehuanca.

The measure also is likely to pass in the Senate, where supporters of the leftist Morales also are in the majority.

Bolivia, like neighboring Peru, permits limited cultivation of coca for legal use in cooking, folk medicine and Andean religious rites. Unadulterated coca is a mild stimulant that counteracts the effects of altitude sickness and suppresses hunger pangs.

"The 1961 convention prohibits coca-leaf chewing. If we don't (withdraw), our brothers and sisters will not be able to take part in this ancestral practice," Choquehuanca said.

The legislators' vote came on the eve of the release of a U.N. annual report on coca cultivation in Andean countries and before Bolivia's former drug czar, Gen. Rene Sanabria, pleaded guilty Thursday in U.S. federal court in Miami to federal cocaine-trafficking charges.

Bolivia, the world's third-largest cocaine producer after Colombia and Peru, acknowledged a few days ago that the area under coca cultivation has grown but said the new figure will be announced in July when the United Nations completes its survey of coca plantations.

The survey was delayed by a recent plane crash in which four U.N. officials were killed.

Opposition lawmakers slammed Morales' request to Congress - submitted without prior notice - and said it ran counter to the country's efforts to combat drug trafficking, although the government insists it will respect Bolivia's commitments in that regard.

The head of the pro-government legislators, Edwin Tupa, defended the measure and said it upholds "Bolivians' dignity," adding that opponents are acting on behalf of the "empire (the United States), which regrettably wants to continue to classify coca leaf as an illegal drug."

The legislation states that Bolivia may rejoin the convention in 2012, but only if the articles that outlaw the chewing of coca leaf - and which contravene the Andean nation's 2009 constitution - are removed.

Morales, an Aymara Indian who came to prominence as the leader of coca growers in the Chapare region, has largely moved away from forced eradication of coca while stepping up efforts against drug traffickers, with record seizures of cocaine.

He has also sought to promote additional legal applications for coca in products including fertilizer and soft drinks.

The president has stated in the past that the chewing of coca leaf dates back to 3000 B.C. and that it is impossible to abolish such an ancient practice.