* South American nation plans to legalize marijuana sales
* Government to grow marijuana if law passes Congress
* Sales to foreigners would be banned to avoid drug tourism
By Malena Castaldi and Diego Barboza
MONTEVIDEO, June 24 (Reuters) - Uruguay's government plans to start growing marijuana soon after a law legalizing sales of the drug passes Congress, but a ban on selling to foreigners will stop the country becoming a drug tourism hot-spot, officials say.
The leftist government announced plans last week to legalize the marijuana market as part of a drive to stop rising crime, arguing that the drug is less harmful than the black market where it currently trades.
The use of cannabis and other drugs is already legal in Uruguay, one of Latin America's safest countries and a trailblazer on liberal lawmaking. The reform being sent to Congress would legalize and regulate its sale and production.
Meeting the smoking needs of the nation of 3.3 million people will require annual production of about 27 tonnes, the government estimates, and the drug will be cultivated in a plantation of roughly 100 hectares (247 acres).
It is not yet clear whether the drug would be grown by the state or by private contractors under license.
Planting should begin in September if the law passes Congress swiftly as expected - despite some opposition from rightist lawmakers, a government source said.
Harvesting would start six months later, said Julio Calzada, secretary general of the National Drugs Board.
"By regulating the marijuana market in the way we're proposing, we're going to undermine the development of trafficking of other drugs," Calzada told Reuters on Saturday. "Our inclination initially is to have production and regulation under state control."
The idea of a state-run chain of cannabis outlets has been ruled out and the drug would initially be sold by closely monitored private businesses.
Registered consumers would not be allowed to buy more than 30 grams (about 1 ounce) per month and foreigners would be banned from buying the drug to prevent the small country becoming a hot spot for pot-smoking tourists, Calzada said.
Uruguay is a favorite holiday destination among Argentines and fashionable beach resorts like Punta del Este are also popular with visitors from neighboring Brazil.
"The idea is that it would only be sold to Uruguayans ... the Netherlands has had to retrace its steps on that issue after years of difficulties with surrounding countries," Calzada said.
The famous coffee shops of Amsterdam have been a haven for drug tourism for decades, but new rules are coming into force that will make it harder for foreigners to buy.
Calzada said cannabis would carry a sales tax, the proceeds of which would fund rehabilitation programs for addicts. State-grown marijuana could also be used for medical purposes.
Pro-legalization groups welcomed the proposal by the government of President Jose Mujica, a former guerrilla fighter, but they are calling for it to allow personal cultivation too.
"As far as we're concerned, legalizing marijuana is an attack on the drugs trade, which is sustained by the policy of prohibition," said Martin Collazo from the Prolegal group.
Mujica's allies control both houses of Congress so the law is expected to pass despite opposition resistance.
Rightist lawmaker Ana Lia Pineyrua said she had "enormous doubts" about how the legislation will be implemented.
"I don't see how we're going to control this when we've failed to control other things," she said, warning that Uruguay risked riling governments battling drug-related violence in South America such as Colombia, as well as the United States.
U.S. President Barack Obama made clear to Latin American leaders at the Summit of the Americas in Cartagena in April that he opposes the legalization of drugs. (Additional reporting by Felipe Llambias; Writing by Helen Popper; Editing by Anthony Boadle)