Somewhere deep in the Kremlin or maybe even at the Soviet Embassy in Washington, a Russian military planner is gleefully pleased, once more with American openness.

"comrade," he exclaims to a colleague, "look at this map I got through the Federal Register! It's the U.S. Navy Trident submarine base which the Americans now plan to build at Kings Bay, Ga."

His colleague comes over to study the official map, which was obtained from a routine notice in the Sept. 19 Federal Register (page 62539).

"notice how they have marked where they will keep their strategic weapons. Look, there will be approximately 55 magazines holding Trident missiles. They have also marked where they plan to put their defensive weapons facility. All that will make it so much easier for our targeters. And here in the channel leading out to sea from the wharves and drydock is something they have labeled a 'magnetic silencing facility.' What is that?"

The conversation is hypothetical, of course, but it is a fact that Russians or anyone else have access to a wealth of defense information from the Federal Register and other government publications.

In this case, it is the final supplement on the required Environmental Impact Statement (EIS) for the Kings Bay fleet ballistic missile submarine support base. The Navy produced its initial EIS for Kings Bay in August 1977. At that time, all it planned to put at the facility was one Poseidon submarine squadron which was being relocated from its forward base at Rota, Spain. Then the Navy decided that the United States should not station all 20 of its giant, new Trident subs on the West Coast at the new sub facility near Bangor, Wash. So Kings Bay was selected in May 1979 as the site for an East Coast Trident base. Therefore, a supplemental EIS was required. The Sept. 19 Register announced its completion and where to write to get a copy.

The EIS is a gold mine of information. Some of it is obvious, such as the fact that some 18,000 Navy personnel, dependents and civilians will be stationed in the area.

But there is useful military information, too. The facility should be ready to accept Trident submarines by 1990 with construction scheduled to begin during fiscal year 1982. When all 10 of the projected Trident submarines are in operation -- by 1998, according to the EIS -- "seven of the crews are considered "at sea" at any one time. That indicates a 70 percent alert rate for the Trident submarines, slightly higher than that of the Poseidons and way above the 15 percent achieved by the Soviets.

When it comes to weapons storage, the EIS is also illuminating. For example, during the initial Trident submarine deployment, assembly of the Trident I missile will continue at Charleston, S.C. Missile storage at Kings Bay will require the 55 magazines. By the way, the EIS says the weapons storage site will be on "about 205 acres" which would "be cleared of all trees and shrubs to provide unobstructed visibility" to satisfy security requirements.

If, in the future, the Navy builds a next-generation missile -- the so-called Trident II -- and decides to place production facilities for it at Kings Bay, then the EIS says an additional "10 new buildings and 100 magazines" would be required.

What about that "magnetic silencing facility?" Well, one official explained that it is nothing secret, but a well-known program in the submarine business going back to World War II. Submarines are metallic and, as such, can be found with magnetic detectors dropped from aircraft or located by metal-seeking bombs or torpedoes. The magnetic-silencing facility, located underwater, takes that magnetic characteristic out of the sub's metal just before it heads out to sea so it cannot be located by a Soviet magnetic sensing device.

A reporter who has fought many battles over getting facts declassified by the Pentagon is bound to wonder whether environmentalists need to know all these details from the Navy. And how much would the Navy tell if a reporter called the Pentagon and asked, "How many magazines for nuclear Trident I missiles do you plan to put down at Kings Bay? And while you're at it, would you send me a map of the base?"