Foreign agents are always trying to crack U.S. diplomatic codes. We know that. We do it too. Idea is to find out what secrets others are transmitting from one embassy to another, or to the various home capitals. Like the case of the stuffed sailfish, for example.

Agents who read U.S. cables are apparently having a tough time trying to figure out the meaning of a recent, strange-sounding Washington-to-Mexico City telegram. In the interests of detente, and to save everybody a lot of time, trouble and misunderstanding this is the cable and the true story behind Operation Sailfish:

RATUIJAC RUEVDFLO0972

1672131 UUU RUEHME

AFAS

R 162131Z Jun 77

FM USDA FAS WASH DC

TO RUEHME/A MEBASSY MEXICO CITY-AGATACHEE

BT

UNCLAS 16th JUNE 1977

AG ATTACHE FM PHILLIPS, FAS

FASTO 59

REF" TELECOM JUNE 15

CONGRESSMAN TAYLOR'S OFFICE INFORMS THAT CONSTITUENTS' STUFFED SAILFISH HAS ARRIVED IN U.S. PLS CANCEL SEARCH. BT

Obviously, that is the kind of cryptic stuff that drives the enemies of democracy wild. What, they are asking themselves, does it really mean? Imagine if the Russians sent the Chinese something like that and we found about it?

Well, it sounds like James Bond stuff. But, alas, it is only the bottom line of a routine request from a voter. It is the sort of thing that pours into Washington and up to Capitol Hill in the hundreds every day. In the case of Operation Sailfish, it involved a Missouri couple who took a midwinter vacation in Acapulco.

During their stay, the husband caught a fish. It was big. He was proud of it. He wanted it stuffed. The Mexican shop he took it to said they would do whatever was appropriate and have it on his mantle in Missouri within six to eight weeks. To make a long story short, it didn't show.

After many frantic, and expensive, telephone calls to Mexican fish-stuffing establishments, the desperate Missouri man turned to his elected representative in Washington. He is Rep. Gene Taylor (R-Mo.). Taylor's staff - like other efficient Capitol Hill operators - didn't bat an eye.

The U.S. Embassy in Mexico City was alerted. The ball fell into the court of the agricultural attache. He, or she, must have done something right because the fish showed up soon afterward in Missouri. Hence, the cryptic telegram canceling the search.

It is all in a day's work for congressional aides, the State Department, and in this case, Agriculture's Foreign Agricultural Service.

One of the people in the middle of Operation Sailfish recalled the case - but off the record - vividly for this column: "We had a missing fish and a missing woman the same day," the U.S. aide said. "I was a little confused and worried that we might wind up having the woman stuffed. I'm glad it worked out."

So the fish is in Missouri, starting glassy-eyed over somebody's fireplace or adorning a torphy wall. The woman has also been found, unstuffed. Cases closed. Tension eased.