U.S. banks have played a major role in arranging more than $350 million in new loans and credits for development of a major oil field in Marxist Angola, according to Angolan officials and banking sources.

Ismael Gaspar Martins, Angola's minister of foreign trade, told Washington Post editors and reporters Monday that Angola warmly welcomes the large investment and participation of U.S. companies in developing his war-ravaged country's depressed economy. He said he hopes others would follow the lead of U.S. oil companies.

"We are sure it can help Angola strengthen its economy," the American-educated Martins said.

The big loan and credit package, which Bankers Trust of New York syndicated and in which the U.S. Export-Import Bank participated, was signed July 26 in Paris and involved five U.S. and 10 European banks. It is believed to be one of the largest such deals for a sub-Saharan African country in many years.

Martins is visiting here as head of a five-person delegation seeking to attract more U.S. investment and promote better relations between the United States and Angola. The two have no diplomatic relations a decade after Angolan independence from Portuguese rule, but U.S. oil companies, led by Gulf, have become increasingly involved there.

His visit comes amid a major Cuban- and Soviet-backed offensive by Angola against anti-Marxist opposition in southern Angola led by Jonas Savimbi. The offensive has stirred concern among American conservatives about the fate of Savimbi's National Union for the Total Independence of Angola (UNITA).

Martins, educated on a Methodist scholarship at the University of Pennsylvania, said his government is "keeping its fingers crossed" that the United States will not provide open aid to UNITA. The 1976 Clark amendment barring clandestine aid to the anti-communist movement was repealed in July.

Martins also stressed that Angola hopes for revival of U.S.-led negotiations seeking independence of South African-administered Namibia and withdrawal of Cuban troops from Angola. The talks broke down last spring.

"We want and are still willing to see the United States play an active role in solving regional problems," he said, stressing that Angola considers the negotiations "suspended" and does not want to abandon them.

The loan and credit package is for expansion of Angola's Takula field offshore at Cabinda in the far north. The field's "rated capacity" of production is 160,000 barrels a day compared with Angola's current level of about 220,500 barrels, a Bankers Trust official said.

The package involves $91 million in two loans for the Angolan state oil company Sonangol and the Cabinda Gulf Oil Co., a $130 million line of credit from the Export-Import Bank for equipment, a $115 million line of credit from the French state financing institution Coface and $17.2 million in other loans from commercial banks.

Martins said the total cost of developing the Takula field is $450 million but did not explain how the remaining financing would be acquired.