The importance of marijuana production to the economy of Jamaica has been grossly exaggerated, according to Jamaican Prime Minister Edward Seaga, who said yesterday in Washington that his government is taking "draconian measures" to reduce production of the illegal drug.

Seaga said that marijuana, or ganja, as it is called in Jamaica, was a "not significant" part of Jamaica's farm economy, employing only 5,000 of the Caribbean island's 150,000 farmers. He also said that marijuana production brings in only $30 million a year to Jamaica.

The U.S. Drug Enforcement Agency (DEA) estimates that 1,850 metric tons of marijuana, with a wholesale value in the United States of about $2.13 billion, was packaged in Jamaica last year for shipment to the United States. The value of that marijuana for farmers and middlemen in Jamaica was about $82 million, according to figures provided yesterday by a senior U.S. drug enforcement official.

Jamaica supplies 14 percent of the marijuana smoked in the United States. It is the third leading supplier after Colombia and Mexico, according to the DEA.

"An awful lot of people in Jamaica derive some economic benefit from marijuana," the official said. "A large proportion of the people that you run into on the island can, for a percentage of the selling price, put you in touch with someone who sells ganja. . . A number of people are living in conspicuous consumption in the country, large cars, houses and so on."

Seaga, who spoke yesterday to editors and reporters of The Washington Post, said that he planned this evening to question Vice President George Bush on the validity of U.S. government statistics concerning marijuana production in Jamaica.

The prime minister said that new laws in Jamaica, which require government licenses for the operation of airports and allow for the seizure of trucks, airplanes and boats, will force a "substantial reduction" in marijuana exports to the United States "by cutting the transportation nexus."

He said "heavy penalties," including large fines and seizure of aircraft and boats, will be enforced. He also said he has introduced a law in the Jamaican Parliament that would keep "unauthorized persons" off the island's tourist beaches. He said harassment of tourists by drug sellers has become "a factor in the tourist trade," an industry vital to the Jamaican economy.

Seaga's comments were challenged yesterday by the senior staff member of the House Select Committee on Narcotics Abuse and Control, who said that money from the sale of marijuana "makes the world go round" in Jamaica and that Seaga has refused to take the stern measures that would eradicate production of the drug.

"Seaga has got a helluva problem down there," said John T. Cusack, the committee's chief of staff. "He just doesn't know how to make a beginning."

According to Cusack and a U.S. government drug enforcement official, Seaga stands to lose considerable political support if he institutes an island-wide program to destroy the marijuana crop, which is an economic mainstay of many rural areas. As an alternative, Cusack and the drug enforcement official said, Seaga has opted for "interdiction rather than eradication."

"This approach has never worked anywhere in the world," said Cusack. "They are tolerating production and the government does not feel it has the political resources to enforce its laws."

In the past three years, Seaga's government has destroyed about 384 acres of marijuana fields, according to the DEA. An agency official said that Seaga's government has shown a new willingness to destroy crops but limits itself to manual destruction methods.

The mountainous topography of Jamaica and the island's fragile tropical environment would make it difficult and risky to use the large-scale aerial spraying that has been effective in destroying marijuana fields in Mexico, the official said.