In this nonshooting war, even a little gunboat ride in the South Atlantic is instructive.

Mother Nature is angry here.

Freezing winds off the snowcapped Andes have risen to more than 40 knots. The Argentine warship pitches and heaves in the troughs between the waves. Rain engulfs us in horizontal sheets. Soon it will snow. We are virtually blind except for the radar.

It is a rotten place for a navy and for a war.

The Strait of Magellan lies just to the north. To the south is Cape Horn and then Antarctica. Over the centuries dozens of ships have found graves in these hostile waters.

On the bridge of the Barradero, a 65-foot boat built in Israel, Lt. Cmdr. Ussinger offers a consoling smile:

"Think how lucky you are. You would not like the conditions farther out."

That is truth. In the Falkland Islands, 12 hours sailing time from here, 70-knot winds and horrendous seas are reported.

We are in the Beagle Channel, named for the ship Robert Fitzroy and Charles Darwin used in the last century in their quest for links in the evolutionary chain. Captain Cook and Sir Francis Drake are other alumni of the South Atlantic.

The Barradero is based at Ushuaia, often called the "last town on earth." The next southern habitation is in the region of the South Pole, a brisk journey of 2,500 miles.

Tonight Ussinger will steam out on a "top secret" mission, not to return until the Falklands crisis has ended.

In Ushuaia harbor we tie up alongside other camouflaged gunboats with torpedoes lashed to their decks. A missile-carrying frigate recently has departed, swallowed up in the storm. The 25th of May, the old British carrier now owned by the Argentines, is said to be out there, not too far away.

Ussinger and his eight-man crew are relaxed, unemotional and apparently confident on the brink of war.

"It will be interesting," he says, "to fight them with their own weapons."

In the case of the Barradero, his statement is a bit off the mark. The boat could have been the product of a United Nations committee. The hull is Israeli, the engines are American, the radar is British and the weaponry--20-mm guns, rockets, and a 12.5-mm antiaircraft battery--is of various origins. It is designed to support and put ashore commandos, but not in weather such as this. There is no room for them below decks. So the Barradero's mission in the days ahead is a genuine mystery.

To some extent that is the case with the entire Argentine fleet. There is no doubt that it is putting out to sea. But, a high-ranking naval officer told me, "we will not go into the mouth of the wolf."

It is unclear whether he meant the Argentines will stay clear of the British fleet or merely will stay clear of British submarines in the blockade zone that extends for 200 miles around the Falklands.

The assumption here is that the British will operate in waters east of the Falklands where they would be out of range of Argentine land-based aircraft. The Argentine fleet, presumably, would operate west of the Falklands, out of range of the British.

But that is all conjecture in the prevailing atmosphere of obsessive secrecy. On flights out of Buenos Aires to towns in the south with military installations, passengers are required to pull down the window shades. Airport transients are hauled away in curtained buses to wait out their plane connections in holding centers miles away.

Three British journalists have spent days in the jail at Ushuaia on "suspicion of espionage." They were arrested for taking notes and photographs at the Rio Grande Airport, where Mirage and Dagger interceptors are parked.

In Ushuaia this week, my interpreter was arrested and detained for three hours for photographing the harbor sunrise: the Barradero and its sister vessels presumably appeared in the picture. An American photographer was picked up the same morning for photographing an innocuous Ushuaia street scene.

There is an amusing contradiction in some of these measures. The only planes hauling civilians in and out of Ushuaia are operated by the Argentine Air Force. They have no window curtains, so we get a fine view of the military forces and preparations at such bases as Rio Grande and Rio Gallegos.

These preparations are going forward with great energy.

Food and ammunition stocks are loaded daily aboard C130s and Boeing 737s for flights to the Falklands from such bases as Rio Gallegos and Comodoro Rivadavia. The Argentines call this their "air bridge" to the 10,000 or so troops on the islands.

A procession of government officials, including President Leopoldo Galtieri, has taken the air bridge this week to Port Stanley, which was renamed Puerto Rivero, and now has been renamed Puerto Argentina. They fly with escorts of Mirage and A4 Skyhawk fighters.

All this activity and tension have had an unfortunate effect on the tourist traffic to Ushuaia and other towns in the south. Magellan gave the region its name, Tierra del Fuego, which means land of fire. He is said to have been inspired by the Indian campfires he observed on his passage through the strait.

It is a beautiful part of the world. Andean peaks rise thousands of feet above the ocean. There are magnificent lakes and exotic mammals--seals, sea lions and penguins, which, however, no longer are found at Ushuaia. The town, it is said, became too noisy for them. But they are sometimes spotted swimming in the Beagle Channel.

Another casualty of this unpleasantness could be this Argentine naval official's version of what he says is a grand strategic design by the United States:

In the event of trouble in the Middle East and the closure of the Suez Canal, it would be necessary to protect the sea lanes for tankers carrying the oil on which Western civilization now depends so heavily. The American fleet in the Indian Ocean would provide that protection south along the East African coast.

Then the South Africans would take over, guarding the lanes around the Cape of Good Hope and into the Atlantic halfway to Argentina. Argentine vessels would take responsibility for safe passage to the South American coast, where the tankers would head north under the protection of various South American navies. In the North Atlantic they would come under the umbrella of the Americans and the British.

It is quite a strategic chain, and it could be broken here in the South Atlantic. If the British and Argentine fleets were to destroy or seriously damage one another, two large holes are torn in the plan.

"But," the naval informant observed with a smile and unexplained optimism, "it may not happen. I think we have no great military problem with the British. It is a diplomatic problem."

That will be seen in the days ahead, as Lt. Cmdr. Ussinger pounds through heavy seas in the little Barradero. Argentine President Visits Falklands for First Time Washington Post Foreign Service

BUENOS AIRES, April 22--Argentine President Leopoldo Galtieri visited the Falklands for the first time today in what officials here described as a continued effort by the Argentine government to rally support for its sovereignty claim as negotiations with Britain reach a crucial stage.

Galtieri, who spent about five hours on the islands reviewing Argentine defenses and meeting with military officials in his capacity as commander-in-chief of the Argentine Army, was reported as saying as his airplane neared the territory that "I am confident and sure that the blue and white will not be lowered," referring to the Argentine flag.

While Galtieri traveled the 400 miles from the southern Argentine coast to the islands' principal town, which the Argentines have renamed several times and now call Puerto Argentina, Foreign Ministry officials met with ambassadors from Western European nations in an effort to soften their opposition to the Argentine takeover.

In London, British Prime Minister Margaret Thatcher said Galtieri's visit to the islands does not affect Britain's sovereignty over them, United Press International reported.

"Nothing General Galtieri can do about visiting the islands today can alter the fact that they have British sovereignty," she said.

Thatcher told Parliament that Britain was making every effort to achieve a peaceful solution of the Falkland Islands crisis but refused to rule out the use of force against Argentina.