The telephone rang on my office desk. ''Ministry of Defense here,'' said a brisk voice, and proceeded to issue an invitation that was, in effect, a message to Moscow and to Europe's peace movement on the eve of planned Easter peace demonstrations.
The ministry offered an unprecedented opportunity to see the most controversial building site in Western Europe - the first of the massive, blast-proof, concrete ''garages,'' due to receive cruise missiles by the end of this year.
At first I heard only the voice's kindly advice to ''bring your Wellies (Wellingtons, or high rubber boots) because it's very muddy.'' Then the message began to sink in: Here was an opportunity to walk through the very ''garages'' whose construction Moscow and the peace movement are striving to prevent.
This visit by US and European journalists was part of the latest in a series of highly orchestrated steps by the British government against Moscow's hopes and the peace movement's recent successes.
So far, the US interim proposal to deploy fewer than the planned 572 cruises and Pershing IIs in Western Europe has not slowed the pouring of concrete at all. The only thing that would stop all work would be a Soviet decision to dismantle all its medium-range SS-20 missiles. Very few here expect that to happen soon, if ever.
So off we went to the US Air Force base at Greenham Common outside London, for an afternoon of some drama, humor, a vast amount of mud, and much food for thought.
''Why are you here?'' a BBC television reporter asked me suddenly from the aisle of the bus.
''Well,'' I said, ''I'm not sure, but I think. . . .'' A camera pointed at me and I wished I had worn a better shirt.
BBC-TV reporter Peter Snow filled me in. ''(Michael) Heseltine is coming . . . by helicopter,'' he said.
So, the defense secretary himself was to be with us. Would he, too, wear ''Wellies''?
The bus did not enter the main gate of the base, but used a back entrance instead. The best-known peace protest camp in Europe is still hanging on outside the front fence. The Ministry of Defense wanted to avoid giving the women of the camp any more publicity.
Out we tumbled into a yellow-brown ocean of mud caused by spring rains. The BBC energetically filmed our boots.
Mouths fell open as a tall man with a lion's mane of blond hair stepped from an official car. This was no less than the new secretary of defense himself, Michael Heseltine, chief government official against the peace groups. A fine figure he made as he strode purposefully across the mud, stopping only to tell BBC television that NATO was the real peace movement and had kept the peace since World War II.
We stood in a narrow concrete bunker. The roof above us was 161/2 feet thick. The walls measured a yard of concrete. In each shelter will stand four giant 78, 000-pound transporters, each carrying four Tomahawk cruise missiles in two aluminum canisters.
The shelters are designed to withstand a 2,000-pound conventional bomb,'' said a helpful US Air Force colonel. ''Each has hydraulically operated doors weighing 80 tons. . . . But if, ah, well, tension, let's say, begins to, well, to mount, the missiles won't be here at all, of course.''
First one ''flight'' (16 missiles) and then perhaps the other five to be stationed here will lumber out of the garage and out into the countryside of Berkshire. The idea is to disperse them under trees and behind hills to make them harder for the Soviets to hit.
If worse comes to worst, the launch center crew will do its thing: A solid-fuel rocket will boost the missiles from launcher to their canisters to cruising speed. The booster will jettison. Fins and wings will unfold, an engine inlet will pop out, a turbofan engine will ignite, and a navigational computer on board each cruise will follow terrain patterns below.
The missile is supposed to fly 1,500 miles to Soviet targets at treetop height to avoid radar. Some experts here worry that the radar guidance might not work over the huge, featureless plain of the western USSR. They also point to test difficulties so far, but Mr. Heseltine told us later that Defense Secretary Caspar Weinberger reassured him at the NATO meeting in Portugal that all is well with the cruise missile.
Squelching across mud and yet more mud, some of it sticking disrespectfully to ministerial pin-stripe trouser legs, we entered the base recreation center.
''Pizza club lunch,'' read a cheerful sign. ''Delicious pizza or hot dog. . . . Full-length movies shown twice daily, 11:30 and 17:30 (5:30 p.m.).''
Inside, Mr. Heseltine spoke forcefully. What Britain most wanted, he said, was for the entire concrete shelter and cruise program to be canceled altogether because the Soviets had decided to scrap the more than 350 SS-20 missiles aimed at Western Europe.
Until that happened, Greenham Common would prepare to receive 96 cruise missiles. If necessary, 64 more would be installed at the US base at Molesworth by 1988.
Why this sudden visit today? To satisfy a natural public curiosity, said the secretary blandly. At another point, Mr. Heseltine happily offered the thought that ''if you have a fence, people always want to know what's behind it.'' The Soviets, he said, had no need to placate public opinion. They could say what they liked, when they liked.
The Kremlin, he said, wanted to divide Europe from the US and to weaken NATO. Britain would consider an interim proposal on deployment, but only if the Soviets acted responsibly and gave up phony double-counting. It would not be enough for Moscow simply to move SS-20 missiles 1,000 miles to the east: they could easily be moved back.
Asked about a US interim proposal, Mr. Heseltine said that the US had consulted with its allies in the proper way. America, he thought, had a difficult role. If it consulted its allies, the press accused it of being pressured by them. If it did not, it was condemned. He supported the ''massive American contribution'' to allied defense.
The Campaign for Nuclear Disarmament peace group? It was masterminded by a small group of professional, politically motivated people. He saw no reason to debate it in public, giving it a wider audience.
Back in the bus, we were blocked for 10 minutes at the back gate by a group of peace camp women lying on the road. Police stood by, then finally dragged them away. The women looked dirty and disheveled, but they attracted the TV cameras.
Their challenge to NATO is far from spent.