For the first time in tis 22 years of operation, this secretive and controversial British owned U.S. military installation was opened today to journalists.

The newsmen, 16 from American and four from British media, were taken on a five-hour closely guided tour of the tiny, wishbone-shaped coral atoll. Many of them had been pressing their governments for years to allow them to make such a trip, only to be rebuffed time and again.

When the tour was over, most of us wondered what all the secrecy had been about. If the Carter administration and the Defense Department wanted to tell the world that not much worth getting excited about was happening here, they succeeded.

The entire day, we saw three aircraft on the ground, one of them a P-3 Orion surveillance plane, and two C-141 transport, one of which carried us here on the six-hour flight from Singapore.

We saw bulldozers, graders and other heavy equipment, operated by shorts-clad U.S. Navy Seabees, being used to extend the island's runway from 8,000 to 12,000 feet. Men and machines were paving an enlarged parking area for airplanes an others wre puting in foundations for eight 80,000-barrel fueltanks.

We saw dozens of small buildings, some of them new, drab concrete-block structures and many more of them tumbledown polywood shacks that are to be replaced by the permanent builidngs.

We saw a century-old Christian graveyard, slowly being absorbed by advancing jungle. This and a deserted church, which we did not see, are the last vestiges of a small local community of coconut plantation workers who were evacuated several years ago to make room for the expanded military installation.

Buried alongside the decaying coral gravestones were a handful of Indian army Moslem soldiers. These men died, apparently of dysentery, while waiting for a World War II battle that bever materialized.

We did not see the wild horses left behind by the coconut planters; the seas turtles that ride the lazy tides into the pale green lagoon, or any more than two or three varieties of the 50 or so bird species that have sancturaries on threeislets at the mouth of the two pronged atoll.

The only other things we did not see, according to the U.S. island commander, Capt. island commander, Capt. Philip F. Yosway, 46, were the interiors of two top-secret communications buildings. These low, cream-ored structures, planted in the midst of a forest of antennae, were off-limits.

Asked whether Diego Garcia provided communications facilities for U.S., nuclear submarines and monitored Soviet submarines, Yosway said stiffly, "we provide communications to U.S. and British ships in the Indian Ocean."

In addition to its communications function, Diego Garcia services U.S. warships and aircraft. Congress has appropriated $55.8 million to expand the air and naval support facilities and another $7.3 million request is under consideration. The total cost, including equipment, is now $173 million.

Although James R. Schlesinger, when he was defense Secretary in 1975, said that the purpose of these support facilities was to enable a U.S. aircraft carrier group to operate in a contingency for a 30-day period, Yosway told us he knew nothing about this.

Yosway refused to comment on such matters as the number of sircraft or ships that Diego Garcia will be capable of servicing when the present construction phase is completed, in 1980.

With an altitude of four feet above sea level and little more than crub vegetation to relieve the tabletop view, Diego Garcia is, as Yosway put it several times, "austere."

A gymnasium, bowling alley, baseball fields and tennis courts offer recreation, while entertainment comes in the form of movies, closed-circuit television and USO shows from the Philippines.

Despite being quite literally in the middle of nowhere - 1100 miles south of India's Cape Comoran and about midway between the Indonesian island of Sumatra and the East African Somali Republic - the 1,400 Americans and their 25 British navy collegues seemed to be in good spirits.

The small British contingent is led by Lt. Cmdr. Arthur G. Portwine, who serves concurrently as commnanding officer, magistrate, customs and immigration officer, Portwine, whom the Americans call the "Brit rep," seemed most concerned with ecological conservation onthe island. "After all," he said, "this place won't always be a military facility and we owe it to future generations not to ruin it."

The United States has been granted use of the island for 50 years with an option to extend for another 20 years. This indicates as clearly as the construction work just how valuable the United States considers Diego Garcia in the high-stakes game now taking shape with the Soviet Union in the Indian Ocean.

This, the real importance of Diego Garcia is not what it is today or what it will be in 1980, but its ultimate potential as a U.S. base in the event of a conventional U.S.-Soviet conflict anywhere in the widespread and sensitive regions that touch onthe Indian Ocean: Africa, the Middle East, the Indian Subcontinent and Southeast Asia.

Since 1971, when the U.N. General Assembly adopted a resolution presented by Sri Lanka to have the Indian Ocean declared a zone of peace, most of the littoral states have been agitating for the tow superpowers to wind down military activity and give up their bases.

The controversy that has swirled around the Diego Garcia project has reemerged in altered form with President Carter's claim last month that the United States has asked the Soviet Union to agree to "complete demilitarization" in the Indian Ocean.

Carter's statement raises afresh contentions by various U.S. critics of the facility that the expansions of Diego Garcia is causing the Soviet Union to react by expanding its military activities in the ocean. The project's proponents, particularly in the Defense Department, have countered that Diego Garcia was necessary to offset the Soviet initiative. This argument is meant to suggest that it is Moscow rather than Washington that is forcing the issue.

But former CIA Director William Colby told the Senate Armed Services subcommittee in closed-door testimony that the Soviet naval presence in the Indian Ocean was "relatively small and inactive." Colby added that any future Soviet increases would result from "the size of th einvestment and forces that we put there."

Retired Rear Adm. Gene Larocque, director of Washington's Center for Defense Information, went beyond Colby, claiming that the U.S. Navy "exaggerates the Soviet naval threat in the Indian Ocean."

In arguing for the necessity of Diego Garcia, former Deputy Assistant Secretary of Defense James H. Noyes said two years ago that the Soviet Union had drastically increased the size of its naval facility at Berbera in Somalia, on the east coast of Africa.

The Pentagon's basic argument onthe need for Diego Garcai is that U.S. ships are required to protect vital iol-supply routes from the Middle East and the Persian Gulf to the West. More than half of the world's sea-borne oil is said to be moving through the Indian Ocean at any given moment.

in the early 1970s, Britain, with the financial support of the United States, forcibly removed between 1,200 and 1,400 inhabitants of the tiny atoll. The islanders, many of whose families had lived on Diego Garcia for generations, wre evacuated to the newly independent island republic of Mauritius.

Britain paid Mauritius $1.4 million to resettle the Diego garcians, but a Washington Post correspondent visiting Mauritius in September 1975 reported that little of this money ever reached the evacuees, most of whom living in abject poverty.

A number of Diego Garcians have appealed to Britain and the United States to be allowed back to work on the U.S. facility. But no one has been allowed to return.

The island is administered from London as part of the British Indian Ocean Territory. Diego Garcia is the largest of three islands that comprise the Chagos Archiipelago. Until 1966, the Chagos along with Mauritius and the Seychelle Islands, were British Colonies. Britain granted Mauritius independence in 1966 and last year the Seychelles, too, were granted freedom.

Britain purchased Diego Garcia from the Seychelles and Mauritius for $30 million. Of that sum the United States, in effect, paid $14 million by waiving research and development costs on Britain's Polaris missle program.