Congress has a chance this week to win one small but important battle in the war against drugs by passing a law giving forest rangers the authority to nail marijuana farmers who grow their crops in our national forests.Fully one-fourth of the marijuana illegally grown in this country is raised on public land - namely in the national forests. In 1980, a mere 5 percent of the pot was cultivated on public land. The amounts have substantially increased because the growers know the chances of being caught and prosecuted are slim.

We have seen a confidential report completed by the Office of Intelligence of the Drug Enforcement Administration that says as much. The pot entrepreneurs are turning to public land because of the increased enforcement and eradication efforts on private property. In the national forests, it is harder to trace the owner of an illegal garden and the growers can plant their patches on acreage that is hard to reach and seldom patrolled by rangers.

The marijuana itself is not the only hazard to health in the forest. The growers protect their crops with booby traps, maiming and killing innocent hikers, campers and wildlife.

To combat the pot growing on public land, Congress in 1986 passed a law allowing the Forest Service to train and arm agents to fight the drug dealers. But incredibly, the Forest Service agents are currently not allowed to work outside the boundaries of the forest. They can't chase a grower over the boundary. They can't search private residences or vehicles. They can't use any of the standard law enforcement methods after a suspect leaves the forest.

Marijuana is not the only drug produced on public land by these forest thugs. Federal agents have found 82 drug labs in the national forests where PCP and speed are turned out. Not known for their environmental consciousness, these amateur chemists dump the chemical waste from their work on the ground and in the streams.

They have worked with smug confidence that the Forest Service was hamstrung. But two men have taken it upon themselves to change that - Sen. Tom Harkin, D-Iowa, and Rep. Ron Wyden, D-Ore.

Harkin co-sponsored a bill with Sen. Richard Lugar, R-Ind., earlier this year to give Forest Service agents the ability to fully investigate, pursue and prosecute any grower who raises marijuana on Forest Service property. No longer would the pot growers thumb their noses as they cross over the forest boundaries. That act has been incorporated into the Senate omnibus drug bill which comes up for a vote this week.

On the House side, Wyden has proved to be relentless in pushing for the same kind of bill. His ideas were incorporated into an omnibus drug act in the House that will also be voted on this week.