When Theodore R. Britton Jr. was named U.S. ambassador to Barbados in late 1975, no one expected him to take his job for more than it was - a political plum appointment by President Ford of a black Republican for services rendered.

What better way to reward a supporter - and enhance the Republicans' image among blacks - than to send Britton to beaufiful Barbados, with its average year-round temperature of 77; give him an embassy, a sprawling residential estate on Barbados' luxurious "Gold Coast," some servants and a chauffeur.

Britton and gratefully accepted that - but only as a start.

Described by former Barbados Prime Minister Errol Barrow as "the ugly American" and reffered to by others here as "the king of Barbados," Britton embarked on a vast enlargement of his domain and won the hostility of several of his embassy aides.

The disenchantment with Britton's performance by some of his staff members has resulted in an investigation by the State Department's Foreign Service Inspector on charges of incompetence.

Sources at the State Department said the President-elect Jimmy Carter has been told of the situation at the Barbados embassy. "It doesn't look like he (Britton) is going to be around much longer," the source said.

Britton alleged to have "punished and humilated" one embassy official who disagreed with his policies. He reportedly angered the Barbados government by becoming too involved in local politics, upstaging government officials at their own gatherings and publicly criticizing Barbados officials.

After one dispute, which resulted in State Department officials choosing a subordinate's proposal over Britton's, Britton asked for the officer's removal, locked him out of the embassy, removed his furniture from his office and left his work papers in an unlocked room.

So far, three of Britton's top officers have resigned or been reassigned from the embassy, criticizing the emergence of a mini-empire out of this fourth class embassy, (the lowest category) that is costing, including expansions, more than $1 million a year.

The mini-empire Britton's critics refer includes Britton's establishment in Barbados of an office for the U.S. Agency for International Development (Aid), although the U.S. does not have an AID program here.

Britton established a liaison between himself and what technically would be the Barbados navy. But Barbados does not have a navy. He established a branch of the U.S. Information Service, although agency staff members say that they are hard pressed to find information to disseminate.

Barbados, with about 148,000 residents, is the smallest Caribbean country to have a U.S. embassy. Yet, the embassy, with 25 foreign service officers working in the consulate and political sections, is rapidly approaching the size of embassies serving much larger countries, such as Trinidad, which has a population of more than a million and just over 50 U.S. embassy officers.

It is not clear whether Britton's business arrangement with a Barbadian contractor is being investigated.According to William Diedrich, the political officer Britton locked out, Britton hired a full-time contractor - whose business is supported solely by Britton - to renovated his residence for nearly $200,000.

In an interview, Britton defended the establishment of the AID and USIS offices, and a defense liason with the putative Navy, saying they were a "credit to the people of the Caribbean since we have those things here."

He said AID was the "local" agency to monitor the $20 million in U.S. loans to the Caribbean Development Bank, which in turn loans the money to needy countries.

But Britton's detractors claim that monitoring of funds did not require a new agency, since the regular embassy staff has done an adequate job.

Although Barbados is considered one of the most stable and peaceful of the independent countries in the Caribbean, shortly after his arrival Britton brought in a contingent of Marines, for the first time since the U.S. mission was established here in 1821.

"Did you notice 'em?" Britton, reclining on a sofa in his spacious office on the third floor of the Canadian Imperial Bank building, asked a visitor. "Did you see what they did when I came in? Yeah, they saluted. It adds a sense of respect to the place."

It did not suit Britton that the generally accepted U.S. position toward the Carribbean was to "lay low," as one foreign servive officer put it, while most of the small Caribbean countries underwent political change.

Although the 50-year-old South Carolina native was not experienced in Caribbean affairs, he says he soon learned what the purpose of his embassy should be.

"We do represent the most powerful country in the world," Britton said during an interview," and we should show it."

Britton began by bringing in the detachment of Marines to guard his embassy. Essentially, they check the purses and bags of the Barbadas citizens who enter, crack jokes with the receptionists, and calute him when he arrives.

The presence of the five Marines brought the first dispute between Britton and then Prime Minister Barrow, who prohibited the Marines from carrying weapons or wearing uniforms on the streets of Barbados.

A wider rift soon developed between Brittin and some of his staff who complained that the ambassador's strict formality was unreasonable and that his policies were irrational.

"The power just went to his head," said Diedrich, who was reassigned following the dispute the Britton.

"He was given to delusions of granduer. For instance, we've got a handful of people working here, but he decides to put out a 35-page telephone directory - expensive - listing everybody's number twice - once under their name, then in a separate section under their title.

"We get red-bordered administrative notices advising us to tell our administrative officer when we want a vacation, things everyone knows except him."

Britton's first test of political judgment came almost as soon as he became ambassador, when it was learned that Cuban Prime Minister Fidel Castro was sending troops to Angola via Barbados.

"You could see them arriving on charter flights from Cuba," Diedrich said. "There were between 10 and 15 flights a week, and it was strange - all males, between 20 and 30 years old, getting off the plane to stretch, and getting back on. Pretty soon we found out, and Washington wanted us to talk to Barrow about it. Barrow told Britton he knew nothing about it, and Britton bought it hook and line."

"That's not true," Britton says. "I knew what was going on.Just remember this: the U.S. wanted those flights stopped, and they stopped. Now I didn't go out onto the runway waving my hands . . . but let it suffice to say it stopped."

Members of Barrow's government say the former prime minister stopped them not at Britton's urging but because he feared knowledge of the flights might hurt the American tourist trade.

Britton was appointed through the personal recommendation of Sen. Strom Thurmond (D-S.C.), after serving in other agencies under the Nixon and Ford administrations.

"I also got the support of Charles Diggs (chairman of the Congressional Black Caucus). How's that for being middle of the road," said Britton.