LAST WEEK Colombian government officials, acting on a tip from U.S. drug agents, seized over 1 million pounds of marijuana that was about to be shipped from that country to the United States. The 574-ton haul, captured in a remote province of the South American country, apparently is the largest quantity of illicit drugs ever confiscated in one raiding operation. Its wholesale value was estimated at about $200 million. U.S. drug officials said the amount equalled from 10 to 25 percent of the marijuana annually smuggled into the United States. Put another way, the marijuana the Colombian authorities seized was enough to make 1 million marijuana cigarettes a day for an entire year.

This record seizure, however, has an even greater significance than that of preventing so much marijuana from reaching the United States. During the last decade Colombia has become a major producer of marijuana and a major way station for heroin and cocaine bound for the United States from other South American countries - and that has great consequence for both its economy and its democratic form of government. The revenue produced by the illicit drug trade - about $1 billion annually - is greater than the value of coffee exports, the country's main legal source of foreign exchange. And the power of the major drug traffickers until recently has seemingly made them immune from arrest and prosecution.

Bolstered by U.S. aid for anti-drug efforts, the Colombian government has been struggling to reduce the malignant influence of drug traffickers within the country. Colombia's attorney general personally directed last week's operation, in which 13 people, including three Americans, were arrested. Tough drug laws and a better-trained (and more corruption-free) police narcotics unit have produced several other spectacular drug busts within the past year. These actions won't end Colombia's problems with illicit drugs and drug traffickers, but they do indicate a new-found willingness among government officials there to deal with the problem. That spirit is the key to the most effective strategy for reducing the flow of illegal drugs into this country: choking it off at its overseas source.