On May 7, 1982, five days after the British nuclear HMS Conqueror had sunk the Argentine cruiser General Belgrano, the submarine's crew was ordered to "general alarm," and "from the sound room came the dreaded 'fast moving contact,' " according to the diary of a British naval officer who was on the sub.

A homing torpedo was believed bearing down on the ship. "This afternoon we all thought the end had come!" he wrote in describing the incident. "I thought to myself 'no' it can't end now . . . . My heart was racing. The sound room continued to report a fast-moving contact and I sat at the head of the wardroom table, sweating, waiting for the torpedo to hit us. The control room was a scene of controlled panic. Controlled because everyone continued to do his job; panic because everyone believed this was the end."

"After what seemed like hours, but was in fact minutes," the crew was told a low-flying airplane, perhaps an Argentine antisubmarine craft, had been seen just 4,000 yards away.

The Conqueror went down to 600 feet below the surface and "ran for an hour." The crew was relieved of action stations after 30 minutes, but for the remainder of the afternoon, "the control room was subdued and the watchkeepers nervous."

Later, after the specialists analyzed the data, the diary reports: "The conclusions were that the airplane must have detected us but probably didn't drop a weapon; the fast-moving contact reported by the sound room may, after all, have been us. I just hope, however, that I have never again to experience those moments."

The swings of human emotion of the men inside the submerged Conqueror -- from fear to relief and sometimes even elation to fear -- are recorded over and over as the crew's struggle to survive under water is portrayed in this extraordinarily detailed, 51-page, handwritten diary.

A copy of the diary was made available to The Washington Post early last month. Material from it was published yesterday in The Post and earlier, in the Nov. 24 edition of the British Sunday newspaper The Observer.

The diary was written by former Lt. Nyrena Sethia, who retired from the Royal Navy in July 1982. He currently is in the Caribbean nation of St. Lucia, according to his mother, who was contacted by telephone last week by The Post. Attempts to reach Sethia were unsuccessful.

The British Defense Ministry has sought to prevent publication in England of additional material from the diary on the ground that it contains security information.

The diary provides a gripping account of the sinking of the Belgrano and information about British intelligence capabilities during the war with Argentina. It also paints a colorful picture of life aboard the submarine, which during much of the war sailed a defensive picket line, protecting the British fleet near the Falklands from attack.

The Falklands war began April 2, 1982, when Argentina occupied the British islands off the southern Argentine coast. Two days later, the Conqueror left its home port at Faslane, Scotland. It did not return until July 3. Failing Equipment

During its three months at sea, the diary shows, the Argentines were less of a danger than the failing parts on the submarine. There were problems with a steam leak on a generator, which cut power and reduced speed, and with radio antennas, which limited contact with the outside world.

Then there were the frequent mistaken electronic signals from the sub's high-technology warning equipment, which often forced it to go to action stations and dive deeper into the ocean to avoid what turned out to be a sonar echo from the Conqueror itself or some other false signal source.

Some of the military equipment described is extraordinary: listening devices that pick up sounds ashore, 13 miles away, and the "bubble decoy" that when fired through a torpedo tube gives off the electronic imprint of a submarine moving away.

The diary also mentions the weapons that did not work: the British AS12 missile, three of which were fired at an Argentine submarine, hit its fin "but did not explode," and the Conqueror's own Mark 8 torpedo, which did not explode when it struck the Argentine destroyer Bouchard.

Finally there were the personal moments: the headaches caused by too much carbon dioxide in the Conqueror because its purifying system was not working and the sub could not surface in the battle area; the exhausted diver who had to be pulled from the icy water while trying to untangle a radio antenna wire that had wrapped around the propulsion screw, and the anger after having spent 3 1/2 hours decoding a "top secret" message from headquarters three days after sinking the Belgrano only to find it consisted in part of "a poor variation of Gilbert & Sullivan's 'Major General's Song.' "

Underlying the periods of tension in a submarine crew, the diary relates, is the extreme vulnerability of the vessel should it be discovered. An easy sitting target if caught on the surface, the sub is not much safer submerged if it is located by modern, acoustic or electronic antisubmarine devices.

The most dramatic day, according to the diary's record of the war, was May 2, the day the Conqueror attacked the Belgrano.

There was "shouting and cheering" in the control room of the Conqueror when, 43 seconds after firing three torpedoes, the crew heard the explosions from the Belgrano, according to the diary.

Seven minutes later, however, "there was a loud bang -- a depth charge. Everyone froze, but the skipper ordered shut-off for counterattack and we took evasive measures . . . . There was silence through the boat -- suddenly it was no longer fun to be doing what we were."

The British sub fled the scene of the attack, with knowledge that two armed, if "decrepit" Argentine destroyers were looking for it. "For an hour we hurtled along at full speed about 500 feet below the surface ," the diary records. "Palms were sweating. You could hear a pin drop. The tension was almost unbearable."

About 18 miles from the attack point, the submarine rose to periscope level and looked around.

"After five minutes, another loud bang, possibly a depth charge," the diary says. "Again, evasive maneuvers and complete silence throughout the boat. I think we were all very frightened -- the destroyers were not transmitting on sonar, so how had they found us, 18 miles from" the spot where the Belgrano had been attacked?

The fear was that the Argentines had a Neptune sub-hunting airplane above the Conqueror, dropping new listening devices in floatable buoys called Jezebels. Were such buoys to locate the submerged sub, the plane could launch its torpedoes, which have sonar homing devices.

"Suddenly it seems that we were hunted. I felt scared, almost trembling, sweating and nauseated. I thought of what we had done -- of the men we had killed. Although we may not have sunk the cruiser, the captain said he had seen flashes of orange flames as the weapons hit. . . . "Scared but determined, we kept going, praying that their destroyers weren't still onto us." Wine in the Wardroom

The Conqueror traveled another hour underwater to a point this time 26 miles from the attack spot, and slowed down to see if its defensive electronic systems picked up surface or air activity.

"To our relief, we had no further contacts and were then able to return to periscope depth to transmit and tell headquarters what we had done."

That evening, the officers "had a glass of wine in the wardroom and spent the evening discussing what had happened."

A message was received from fleet headquarters, " 'Brandy is for heroes' -- from Oscar Wilde's 'Port is for gentlemen, brandy is for heroes,' " the diarist notes.

During late April, May and early June, the Conqueror, according to its diarist, faced dozens of tense moments, most of which were self-generated.

The first "excitement" recorded five days out of Scotland came when the nuclear reactor failed briefly, and the submarine began to sink. About 2,500 gallons of excess water used to stabilize it while submerged had to be pumped out. "After pumping that out, we eventually started to come up. There were a few relieved expressions."

On May 5, however, a really serious problem developed: a leak in one of the steam generators that drive its propulsion system. That "probably is going to require us" to drop to "about 37 percent power, not much more than 15 knots. This could be disastrous -- suicidal -- if attempting evasive maneuvers after an attack. Christ!" the diarist writes, "I hope politicians see sense and call it a day. The ship's company remain nervous and sudued, though performing their duties admirably. The whole thing seems to have bought us all closer together than ever before . . . . The worst part is waiting, without knowing what is about to happen, whether we are about to be depth-charged again."

The leak eventually was patched.

The next day brought more bad news. "The electrolyzer which processes the carbon dioxide and restores oxygen to the air in the submarine is now dead and we have only 26 days' oxygen on board," the diary reports. That means "we are having to snort put up a visible snorkel to take in surface air whenever we can," a maneuver that put the vessel close to the surface and makes discovery by the enemy easier.

The heavy presence of carbon dioxide in the air caused recurring periods of headaches for the crew. On May 11, the diary reports, "Oxygen is very low tonight and CO2 high -- so not only can I not light any candle, but CO2 is giving me a headache." Again," CO2 went up to 1.8 percent in the evening" of May 19, the diary reported, "so we all have headaches."

The radio antennas were another major problem. A submarine, when deeply submerged, cannot have radio contact with the outside world as normal radio waves do not travel through water. Submarines handle their normal communications by coming near the surface and sending or receiving messages through wire antennas stretched out behind the craft or mast antennas attached to the superstructure of the sub. Continuous Wire Trouble

The Conqueror experienced continuous trouble with all its wires. The worst situation began on May 17, when "in the evening we lost high frequency reception on the floating wire. Headed some 60 miles to the east and into hopefully quiet waters and surfaced to change wires. Four hours surfaced yielded three useless wires, so we dived again while the geniuses tried to fix them. It was a little nerve-wracking, remaining on the surface, a sitting duck."

The next day they surfaced three more times. "Certainly pushing our luck, but we didn't get caught. Unfortunately, all three wires are still useless." To solve the problem, the submarine was "having to spend several hours at periscope depth about 10 feet to 20 feet below the ocean surface and make several runs at each signal to be able to power an intelligible copy. So at present we are wallowing and awaiting."

On May 22, a new wire problem developed. "The end of the old RHG wire now appears to be caught up in the screw and is making a hell of a noise." Noise at sea can easily give away the location of a submarine. Thus, "we are going to have to surface and put divers down; very worrying. Can nothing go right for us?"

The next day the sub surfaced in the evening "to put a diver down to investigate the line; it was most unpleasant and nerve-wracking but the diver bravely spent 20 minutes in the cold rough water and managed to cut free 150 feet of the wire. A small loop remains caught round the screw, but the sound has been considerably reduced . . . . The diver was pulled on board suffering from exhaustion and we all think he deserves a medal; however, after a tot of rum he was back to normal." Unexploded Bombs

One danger facing the ships in the Falkland fighting was the failure of missiles and bombs to explode when they hit their targets. On May 23, the diary reports, the HMS Antelope had been hit by a bomb that "had failed to detonate." The next day, however, it was reported, "the Antelope's bomb exploded and miraculously killed only one person." The ship sank on May 25.

Repairs to British ships were a problem, as the diary's description of the submarine HMS Splendid's problems shows.

On May 8, it was reported "poor, old Splendid has had some generator problems and is returning to South Georgia an island south of the Falklands taken earlier by the British for an airdrop, so that will take her out of the fray for a couple weeks." Two days later, the diary notes, "Almost unbelievably, the generator part which was airdropped to Splendid broke up on hitting the water and also sank, possibly due to a faulty parachute."

Perhaps the most personal sections have to do with the crew's attitude toward its sinking of the Belgrano in the weeks afterward.

On May 6, with news that there were "over 800 survivors," the diarist wrote: "Does it make one feel any better, knowing that we killed less than we originally thought? Can we believe that things are not so bad as only 200 died instead of 1,000? Do the numbers make the deed any less terrible? I think not."

One week later, May 9, with the Conqueror in the battle area, the diarist reported, "Today being Sunday we all joked that it would probably turn out to be another day for a 'bit of slaughter.' Church in the wardroom had a higher attendance than ever before . . . ."

By May 20, there was a pause while the British prepared for their counterinvasion. Aboard the Conqueror, "we are having a T-shirt designing competition," the diary reported. "Some good ones are appearing, including one with the motif, 'I killed 175 Argentinians,' an amusing if sick sequel to the Belgrano incident! It's funny how remote that affair seems to be looking back at it 18 days ago. It is still very much on my mind, but I am now relaxed when I think of it. I think most people are actually proud, in a way . . ."

On June 17, three days after the Argentine force on the Falklands surrendered, the Conqueror was on its way back home. "Today a crowd of about 20 gathered in the control room to listen to the tape recording of our attack on Belgrano," the diary reports.

"It was amazing! Every action was perfect, like something out of a text book, every order so lean and the tension unbelievable. It certainly brought back memories. It would make and excellent training tape. As it progresses, the orders become crisper until at the moment of fire, they are being shouted out. The cheering afterwards is phenomenal!"