Florida officials have authorized the spraying of marijuana patches with paraquat, a toxic herbicide that created a panic among marijuana smokers several years ago because of fears that the poison could damage smokers' lungs.

The spraying by Florida law enforcement agencies will be the first time that paraquat will be used on a regular basis to destroy marijuana in patches in the United States. After the scare about marijuana tainted with paraquat in Mexico, Congress banned use of foreign aid funds for spraying fields abroad with paraquat, although Congress repealed the law last year.

Florida law enforcement officials said the spraying will pose no risk to humans. However, Chevron Chemical Co., the primary distributor of paraquat in the United States, has warned that use of the herbicide against marijuana was a poor idea and is probably illegal.

"The product label bears the word 'POISON' and the skull and crossbones insignia, but terrifying people in order to change their social behavior is not a registered use" of the herbicide, said Earl L. Stripling Jr., a Chevron vice president, in a letter this spring to the Drug Enforcement Administration. "Thus if we are dragged into any legal problems, we will take the position that the use was illegal and ask the government to indemnify us."

The National Organization for Reform of Marijuana Laws will sue Florida to block the spraying program, said Kevin B. Zeese, executive director of NORML.

Florida Gov. Bob Graham and Attorney General Jim Smith say the spraying is the best way to eradicate large plots of marijuana and will be an example to Colombia and other Latin American countries considering the use of paraquat. "It is inconsistent to solicit other countries if we are unwilling to use it in our own," Graham said.

"Whatever damage from paraquat would be incremental compared to the damage from smoking unsprayed marijuana," said Don North, spokesman for the Florida attorney general. North stressed that fields that are sprayed will be guarded so that no tainted marijuana will reach the streets. He said that even if the plots must be guarded round-the-clock until the plants are "down and dead," spraying will be cheaper than uprooting and burning the marijuana.

North and other Florida officials stressed that paraquat already is used widely in raising crops such as wheat, soybeans and cotton. But when farmers use paraquat, they spray before the crops are planted. Only rarely--as in the case of sugar cane--would paraquat be applied directly to a crop, and then the edible portion would be protected from the chemical, said G. Michael Marcy, a Chevron spokesman in San Francisco.

"It's a toxic product, and if you abuse it, it'll do some harm," Marcy said.

James L. Harley, a deputy director of the Florida Department of Law Enforcement, said licensed applicators would begin spraying from trucks or backpacks as soon as a suitable plot--one with more than about 1,000 plants--was found.

State officials insisted that even if some marijuana laced with paraquat were to reach the market, smokers would not bear any significant risk. They cited studies indicating that the dangers of paraquat had been overestimated when tainted Mexican marijuana was distributed in the United States in 1977 and 1978.

Medical experts say there is little evidence either that paraquat is dangerous or that it is relatively safe. Dr. John A. Liddle, chief of the toxicology branch of the Centers for Disease Control in Atlanta, said CDC researchers could not find a single case of anyone being hurt by marijuana contaminated with paraquat. He said that paraquat can injure smokers' lungs, but probably poses less risk than marijuana smoke itself whether or not it contains paraquat.

However, a National Academy of Sciences study published earlier this year concluded that "an individual who continued to smoke paraquat-contaminated cigarettes would be a candidate for serious lung injury." The report added that while paraquat has not been proven to be dangerous, "if exposure is sufficiently intense over years, respiratory insufficiency, disability, and death may reasonably be expected to ensue."

Scientists disagree on the medical risks of marijuana itself. Many say that although much research remains to be done, marijuana, like other drugs, poses significant health problems. An estimated 22 million Americans smoke marijuana regularly, and 11 states have passed laws abolishing criminal penalties for possession of small amounts of marijuana.

Georgia may also use paraquat on very large plots, but few are expected to be so large as to require it, said Charles S. Stone, a special agent in the Georgia Bureau of Investigations. Stone said agents sprayed a several-acre field last fall with paraquat, apparently the first domestic use of the herbicide against marijuana.

Zeese, of NORML, said a considerable amount of marijuana is grown in Florida, although the state does not account for as much as California. The Florida crop has been estimated to be worth $400 million a year, making it the state's second-largest cash crop after oranges.