''What we have learned as a result is that we're going to have to strike some sort of balance here if we want to keep the cactus as a symbol of Arizona,'' said Terry Johnson, who is coordinator of the Arizona Natural Heritage Program.

Under a 1929 Arizona state law, the mutilation, removal or destruction of any native plant species is punishable as a criminal offense.

It is a legal mandate that Mr. Countryman, who is commonly referred to as the state's chief ''cactus cop,'' takes seriously. In recent years, he has arrested two of his neighbors, one of his enforcement officers and the president and vice president of a native plant society that Mr. Countryman helped organize. In each case, the suspects were charged with illegal possession of protected plant species.

Ordinarily, that is a misdemeanor. But if the plants are worth more than $100 the charge is grand theft, a felony, and a 15-foot-tall saguaro is worth as much as $350 in the legal market. Life-Threatening Job

Predictably, Mr. Countryman has made a few enemies along the way. Earlier this year, he said, someone shot an arrow at him as he bent over to tend a flower bed in the garden behind his home in west Phoenix. It narrowly missed and stuck in the wall over his head. Earlier, the brake fluid was mysteriously drained from his car, and stones have been pitched through the window of his truck, he said.

''People always ask me how it is I can risk my life over a plant,'' Mr. Countryman recalled in an interview. ''Well, it's my job. And the situation has just gotten to the point in recent years where it's become life-threatening.''

In fact, last year employees of the compliance division of the state Agriculture and Horticulture Commission, the group that Mr. Countryman supervises, began to receive training in law enforcement techniques. Mr. Countryman said he has a shotgun in his truck, and usually carries a pistol.