Most of the 44 mercenaries held by South African authorities after a bungled coup attempt yesterday on the island nation of Seychelles are former members of elite units in the Rhodesian and South African armies, according to news reports here and information provided to American journalists.

An American, identified as Barry Francis Gribbon, 26, of Miami, is believed to be among the mercenaries who were arrested after they abandoned their attack on the Seychelles airport and flew to South Africa in a hijacked Air India plane, American journalists were told.

South African news reports identified many of the mercenaries as being former members of elite Rhodesian military units, including the Selous Scouts, the Rhodesian Light Infantry, and the Special Services Battalion. The newspaper Die Transvaler quoted an unidentified former officer of the Rhodesian Special Air Services unit as confirming that between 30 and 40 percent of the force consisted of former members of various Rhodesian units.

Meanwhile, American journalists were told that at least one of the mercenaries was a former member of a special South African commando force.

There is, so far, no evidence of official or direct South African involvement in the operation. But it is still not known who recruited the mercenaries, who are mostly in their 20s, nor who put up the money for the scheme.

At the United Nations, a spokesman said that Seychelles Foreign Minister Jacques Hodoul sent a telegram to U.N. Secretary General Kurt Waldheim saying the mercenaries were "presumably of South African origin," the Associated Press reported. Hodoul said the "ruthless attack" was committed "upon a peace-loving people who above all are struggling with determination to overcome the legacy of colonialism and underdevelopment."

The spokesman said Waldheim, in a statement, said the "criminal act, which endangered innocent lives, constitutes a flagrant violation of fundamental principles of international law."

Some observers believe that the leftist government of Albert Rene was tipped off about the arrival of the would-be coup-makers, accounting for the quick and effective response of the Seychelles defense force. An eyewitness report on the attack by former Rhodesian Army officer David Conradie in The Citizen, a Johannesburg newspaper, described how Seychelles Army troops quickly arrived at the airport and drove many of the mercenaries into a wing of the airport building.

Conradie, who was said to have been vacationing in the Seychelles when the attack occurred, told the paper he also saw a detachment of North Korean troops arrive at the airport and launch the assault that ended the resistance of the mercenaries barricaded in the airport wing.

In Washington, State Department officials said that while they had received some indirect reports of North Korean military advisers in the Seychelles, they could not confirm that any North Korean military personnel were on the islands.

South Africa has become a haven for white mercenaries who fought in various African wars, mostly on the losing side. In the past 18 months, many who fought with the Rhodesian Army have come to South Africa to join its defense force or "retire" into civilian life.

Gribbon, a U.S. Army veteran, served in a Rhodesian Army unit during the war there and then came to South Africa after Rhodesia became Zimbabwe, according to information supplied to American journalists here. He signed a one-year contract and joined a special South African reconnaissance and cross-border operations unit base in Durban called "Recce Six." He was to have begun a job as a salesman for office equipment last Monday, associates told one journalist.

Passengers who were on the hijacked plane were quoted in the English press here as saying they were told that the mercenaries' weapons, stashed in their luggage, were detected at the airport in the Seychelles when they landed, dressed in civilian clothes and posing as a rugby team on vacation. This forced them to put their plan into operation sooner than they had intended, the mercenaries told passengers.

After commandeering the Air India plane in an effort to escape, they apologized to the 79 passengers on board and were very polite, according to the passengers' accounts in the local press. One of the mercenaries reportedly told a fellow passenger, "You have saved our lives."

South African police refuse to disclose the names or nationalities of the men they are holding in Pretoria Central Prison while they pursue "an intensive investigation." Officials have said they will be tried as hijackers.

Meanwhile, police in Swaziland, where the mercenaries boarded a scheduled flight to the Seychelles yesterday, began investigating how the mercenaries were able to take weapons onto the plane.