The plane used by the U.S. Embassy in South Africa may become the focus of a much larger international furor following South Africa's charges that it was used for espionage purposes.

The Rhodesians already ahd charged that the aircraft was used fo spying on vital Rhodesian military installations while it was used to fly various American and British envoys involved in the Rhodesia negotiations during the past 18 months.

The aircraft was also used to ferry Western envoys between Salisbury and black African capitals all across southern Africa. This raises the possibility that the twin-engine craft may have been involved in collecting photographic intelligence while flying diplomats to Angola, Zambia, Botswana, Tanzania and Mozambique.

If true, the plane's activites may compromise U.S. relations with a number of black African states as well as with white-ruled South Africa.

Earlier this week, the National Observe published here in Salisbury ran a front-page story asking: "Was a spy camera used to photograph Rhodesian Air Force installations when British and American diplomats flew to Salisbury for surprise settlement talks in March?"

"It could have been," the weekly newspaper continued, "beacuse on the plane with London representatives Mr. Robin Renwick and America's ambasador to Sambia, Mr. Stephen Low, was a sophisticated aerial survey camera."

The newspaper identified the American plane as a "Beech 2000" bearing theletters and numbers SPAR 75 and said that when it left here on March 22 leaving the envoys behind, it circled New Sarum Air Force Base outside the captial twice before heading for South Africa.

Rhodesian government officials would not comment today on the South African allegations that the plane out outfitted with an aerial spy camera. But the National Observer quoted an unnamed highly placed government source as saying "this is an appalling state of affairs.

"Even if the camera was not used - which is definitely questionable - the mere fact that it was on board the same aircraft as two visiting diplomats is a distinct breach of diplomatic protocol."

U.S. Ambassador Low and British special envoy John Graham as well as Renwick frequently employed the Pretoria embassy plane on their exhausting trips around the different African states in their attempt to sell the British-American proposals for a peace ful settlement to the Rhodesia dippute.

It was used on a regular basis because there are no air connections between Salisbury and any of the black African capitals concerned. There are few commercial flighs between the various =front-line" states that support the guerrilla effort to oust the white-dominated Rhodesian government.

Observers here also recalled that U.S. Ambassador to the United Nations Donald McHenry, who led the five Western nations in negotiations with South Africa over Namibia (Southwest Africa), occassionally used the Pretoria embassy plane on his tours of southern Africa.

There is no hard evidence at this point that the plane was outfitted with an aerial camera on any of these trips. But it would appear to have been an ideal occasion for photographing under the cover of an important diplomatic mission. CAPTION: Picture, South Africa impounded a C12, the military version of this Beechraft turboprop. AP