Cuban troops are protecting American business interests in Angola from attacks by antigovernment rebels supported and armed by the United States and South Africa.

About 2,000 Cubans, part of an estimated 35,000 troops sent to Angola by Fidel Castro, are stationed here around the Gulf Cabinda oil installation, the country`s largest, which was the target of a failed sabotage attempt by South African forces last year.

The airport terminal building, municipal water supply and an electric-power facility in nearby Cabinda have been the target of attacks by saboteurs this year.

The U.S. has no formal diplomatic relations with Angola and has supported efforts to overthrow its Marxist government since independence from Portugal was gained in 1975.

Asked if protecting American interests was what he expected a Cuban soldier to do, Capt. Pedro Valdez Alfonso said no. ''We are not here to protect Americans, but Angolan economic targets,'' he said. ''Everything that smells of the enemy we will annihilate.''

Gulf Cabinda is 49 percent owned by Chevron Corp. and 51 percent owned by Sonangol, the Angolan government oil company.

About 200 Americans work at the facility, where daily production totals 190,000 barrels of oil and 6,000 gallons of liquid propane gas.

The fact that Cuban soldiers protect Americans and American economic interests in a Marxist country from attack by an American ally and rebels armed with American weapons points up the confounding and contradictory nature of U.S. policy.

The U.S. is Angola`s No. 1 trading partner. It consumes, with the help of other Western nations, the majority of the Angolan oil exports.

Angola also is the third-largest outlet for American products in Africa. More than 30 major U.S. corporations engage in business here and the government says it would welcome more.

Yet despite Angola`s mixed economy and support from traditionally conservative American business interests, the U.S. government views the country as a Soviet client.

The U.S. has provided arms and financial assistance to antigovernment rebels, but it has done little to woo Angola to the West.

When the Portuguese pulled out of Angola in 1975, the country was left in nearly total disarray.

Buildings, automotive equipment and vital records were destroyed. There were about 45 doctors left and a mostly uneducated and unskilled population.

Although the U.S. and other Western powers were reluctant to help, Cuba was not. It sent in 400 physicians and began a literacy program. It also sent soldiers.

They came at the Angolan government`s request after the South Africans, supported by rebels from UNITA, the National Union for the Total Liberation of Angola, launched a drive in late 1975 on Luanda, the national capital.

With Cuban assistance, the attack was repulsed.

Both UNITA and South Africa have continued their campaign against the Angolan government, and Cuban forces have remained in the country in varying numbers, providing defense of areas north of the 15th parallel, including Cabinda.

South Africa, with U.S. backing, has set the removal of the Cubans as a precondition of its granting of independence to Namibia, the sole remaining colony on the continent.

But Angolan officials say the Cubans will stay as long as South Africa continues its efforts to destabilize the country.

Among the Cubans` duties are to stand guard around--but not fraternize with--Americans brought in by the government to run the country`s oil industry.

Tom Willoughby, operations manager at Gulf Cabinda, said his American workers are not permitted to leave the installation compound, ''except on an absolute-need basis.''

He described the compound as a self-contained community with many of the comforts of the U.S. as well as its own water, electric and microwave telephone system and a nine-hole golf course.

American employees work 28 days, then are off 28 days, and earn 45 percent more pay than their counterparts in the U.S.

Willoughby said he saw no need for the company to cave in to pressures from conservatives in the U.S. who want American business interests to pull out of Angola.

''The fields would not shut down because there are others here who could run this facility,'' he said.

Asked about concern among workers that they may be the target of attack by antigovernment elements, Dwayne Greenwell, of Georgetown, Tex., said:

''People come in knowing what the situation is. But they have some anxieties.''

He said he thought ''it would be advantageous for the U.S. to have closer ties with Angola. We have ties with Russia and China. You don`t have to be friends, but if there is no contact, you can`t talk.''