A civilian transport aircraft, leased to diamond mining operations in Angola and crewed by Americans and Canadians, was attacked and damaged by a surface-to-air missile fired by antigovernment rebels in the southern African country, the plane's owners have charged.

The attack, which occurred shortly before the March 1 kidnaping of about 150 foreigners working at a diamond mine in the same area of northeast Angola, has highlighted the continuing use of economic warfare by UNITA rebels in their 10-year conflict with Angola's Marxist government.

The owner of the damaged plane, IAS Guernsey, a joint Anglo-Irish company, has protested to the State Department about U.S. aid to the rebels, including recently reported shipments of more sophisticated missiles than were previously in UNITA hands.

The company fears the missiles will further endanger western nationals working in Angola, according to IAS managing director Gerry Connolly.

In talks with the State Department in Washington last month, Connolly said, "We pointed out to them that we are operating American-built aircraft, with American and Canadian crews. We wanted them to be aware that if there was any question of the United States" providing sophisticated armaments, that UNITA leader Jonas "Savimbi will use them against our civilian aircraft and civilian personnel."

According to Connolly, one of three Lockheed-built Hercules transports the company leases to Diamang, the Angolan government diamond concern, was flying at 8,000 feet shortly after takeoff from the eastern Angolan town of Dundo on Feb. 10 when fire broke out in two of four engines.

After returning to the airstrip for an emergency landing, the plane's starboard wing fell off.

The cause of the fire was believed at the time to have been "catastrophic engine failure," Connolly said in a telephone interview from Ireland.

But the engines were sent back to London, where the conclusion of company examiners that a missile had been involved led to the protests in Washington.

Last week, Connolly said, ordnance experts appointed by insurance investigators confirmed that "the damage was caused as a result of an impact by a missile."

No injuries were reported in the incident.

Its assumed cause, based on examination by the specialists of fragments of foreign metals taken from the engines and studies of the point of impact, was independently confirmed by aviation insurance sources here.

Asked about Connolly's complaint, a State Department official in Washington said that a travel warning is in effect advising U.S. citizens of the danger of travel in Angola outside the capital of Luanda.

Suggestions that the missile that struck the plane could have been fired by Angolan government forces were dismissed by Connolly as unlikely.

"Our airplanes fly the same route five or six times a week," he said, "and have been doing so for the past 15 months. The likelihood that the Angolan military would be taken by surprise is highly speculative."

UNITA -- the National Union for the Total Independence of Angola -- is believed to have a quantity of Soviet-manufactured SA7 missiles, purchased on the international arms market or from U.S. allies, with U.S. and South African funds.

Although the rebels in the past have claimed to have shot down helicopter gunships used by the Angolan Air Force, and at least one American-owned civilian plane was destroyed on the ground in 1985, the February incident is the first reported hitting of an airplane in flight.

The rebels have complained that the shoulder-fired SA7s are unreliable and that their range -- less than two miles -- is insufficient to thwart attacks by the heavily armored, Soviet-made gunships.

The February attack against the IAS plane came before a shift in U.S. policy in March led to the first direct shipments of highly accurate, U.S.-made Stinger missiles to UNITA and to anti-Soviet rebels in Afghanistan.

IAS, which Connolly said employs about 70 foreigners in Angola, of whom about 25 are American and Canadian pilots and other flight crew, is one of a number of foreign companies that operate in Angola.

The largest foreign operation -- petroleum installations operated by Gulf Oil in the Angolan enclave of Cabinda -- came under attack a year ago this month by South African commandos masquerading as UNITA forces.

The diamond-mining region of northeastern Angola has been a frequent UNITA target during the past two years, a period that includes four separate kidnapings of British and other foreign citizens who help operate the lucrative diamond mines.

The first three incidents resulted in the hostages being marched for hundreds of miles to Savimbi's headquarters in the southeastern part of the country, where they were released.

Following the kidnaping in March by a UNITA force estimated at 500 rebels at the mining town of Andrada, the hostages were marched for two weeks through the Angolan bush and across the border into Zaire before being released.

In interviews in Angola last fall, Western European businessmen said that attacks by UNITA commando units had made roads outside a small perimeter around Luanda largely impassable.

Exporters and manufacturers in the capital noted increasing difficulty in shipping raw materials by truck from the interior, and in transporting supplies and consumer goods to provincial capitals.

Western embassies in Luanda early last year began restricting diplomats and employes from road travel outside Luanda, advising that all necessary travel be done by air.