San Francisco — The ''narc raid'' is an established feature of American crime-fighting lore. And the swift descent of helicopter-borne narcotics agents on a marijuana ''plantation'' has taken its place alongside the street-level ''bust'' in the sometimes theatrical but deadly serious work of drug-enforcement agencies.
For the past week and more, such an airborne drama has been played out in the forested hills of Humboldt County in California's coastal north country. The area has among the heaviest concentrations in the US of the hemp, or cannabis, plants that are the source of marijuana.
Using a light airplane to locate the illegal, hard-to-spot ''pot farms,'' officers of the California Bureau of Narcotic Enforcement are seizing and burning as much of this fall's crop as possible before it can be harvested and sold, says Robert Manning, chief of the bureau. A $25,000 grant from the US Drug Enforcement Administration is providing most of the financing, and Mr. Manning indicates the raids will continue ''as long as the money holds out.''
The current effort in northern California is not part of the major new anti-marijuana effort announced Sept. 30 by the Reagan administration. That drive reportedly will utilize military helicopters and special state-federal strike forces, augmented by National Guard troops, against those who produce a US marijuana crop estimated as worth from $10 billion to $15 billion a year.
Although he says that as much as 10,000 pounds of unharvested marijuana have been seized by armed, machete-wielding agents in the past couple of weeks, Jerry Smith, director of the California bureau's San Francisco office, admits that the effort will only ''scratch the surface.'' He points out that most marijuana plantations contain 100 or fewer individual plants and thus are difficult to find.
The strategy, Manning explained, is to ''make the risk of growing marijuana so high and the lack of return so significant as to render it not worth the effort.'' He added, ''We're just doing the best we can with what we've got.''
No arrests had been made as of Oct. 20, said Smith, although Manning indicated that narcotics officers are under orders to make arrests where possible. Growers usually have plenty of time to hide or flee when the helicopter approaches.
The marijuana crops are not being sprayed with the controversial herbicide paraquat or any other sustance, the California officials said. In fact, paraquat has been sprayed only once in the US - on a field in Florida.
As for catching those who are distributing the marijuana, Smith says ''We haven't been coming across any middlemen'' in the current raids.
Reminded that some sources say many of the US marijuana growers are ''ordinary people who are not really criminal types,'' Manning said he doesn't see it that way. ''What they are doing is illegal, and they are criminals.''